feat(studio): clearer store + channel switcher + approvals & welcome polish

- store: repair the filter dialog crash (a Spacer lived directly in
  AlertDialog.actions, which is an OverflowBar, not a Flex — it threw
  and rendered a broken dialog). Buttons now sit in a Row.
- store: promote the module-store manager from a bare icon to a
  labelled 'Add store' button, and fully localize the dialog (DE/EN).
- store: add a curated 'Suggested stores' shelf with one-click
  add/remove (first entry: Recl∆Im). Each suggestion is probed for
  reachability and shows 'not available yet' until its index is
  published, instead of failing only on click. Fail-open on network
  errors so a transient hiccup never hides a real store.
- sidebar: the channel pill is now a one-click channel switcher
  (menu with per-channel running state + active check; switching
  writes ~/.chain/current-channel, restarts the daemon, and Studio
  repoints to the new channel).
- approvals: lead the card with the human prompt ('what am I
  releasing?') and demote the flow/step id to a metadata line; clear
  fallback when the step left the prompt empty.
- welcome: tidy the docs grid into equal-height paired rows with a
  full-width trailing card for the odd one out.

Signed-off-by: flemming-it <stefan.a.flemming@googlemail.com>

lib/widgets/chain_stores_dialog.dart

@@ -3,11 +3,15 @@
 // every store's modules into one searchable index, so adding a store
 // (e.g. a domain app's published modules) makes them appear in the Store.
 
+import 'dart:async';
+import 'dart:io';
+
 import 'package:chain_client_sdk/chain_client_sdk.dart';
 import 'package:flutter/material.dart';
 
 import '../data/error_presentation.dart';
 import '../data/hub.dart';
+import '../l10n/app_localizations.dart';
 import '../theme/tokens.dart';
 
 class ChainStoresDialog extends StatefulWidget {
@@ -28,10 +32,46 @@ class _ChainStoresDialogState extends State<ChainStoresDialog> {
   final _url = TextEditingController();
   bool _busy = false;
 
+  /// Reachability of each suggested store's index URL. `null` while the
+  /// probe is in flight, `true` once a response arrives that the hub
+  /// could parse (fail-open: network errors also count as `true`, so a
+  /// transient hiccup never hides a real store), `false` only on a
+  /// definitive 4xx/5xx — i.e. "the provider hasn't published it yet".
+  final Map<String, bool?> _reachable = {};
+
   @override
   void initState() {
     super.initState();
     _reload();
+    for (final s in _kSuggestedStores) {
+      _reachable[s.url] = null;
+      _probe(s.url);
+    }
+  }
+
+  /// One-shot HEAD-ish probe of a suggested store's index. Fails open:
+  /// only a clean 4xx/5xx marks it unavailable; connection errors and
+  /// timeouts leave it available so the hub stays the real authority.
+  Future<void> _probe(String url) async {
+    if (!url.startsWith('http')) {
+      if (mounted) setState(() => _reachable[url] = true);
+      return;
+    }
+    bool available = true;
+    try {
+      final client = HttpClient()
+        ..connectionTimeout = const Duration(seconds: 4);
+      final req = await client.getUrl(Uri.parse(url));
+      final resp = await req.close().timeout(const Duration(seconds: 5));
+      available = resp.statusCode >= 200 && resp.statusCode < 400;
+      await resp.drain<void>();
+      client.close(force: true);
+    } catch (_) {
+      // Offline / DNS / timeout — fail open. The add path will surface
+      // any real error if the operator clicks through.
+      available = true;
+    }
+    if (mounted) setState(() => _reachable[url] = available);
   }
 
   void _reload() =>
@@ -44,23 +84,29 @@ class _ChainStoresDialogState extends State<ChainStoresDialog> {
     super.dispose();
   }
 
-  Future<void> _add() async {
-    final name = _name.text.trim();
-    final url = _url.text.trim();
+  Future<void> _add() =>
+      _addStore(_name.text.trim(), _url.text.trim(), fromFields: true);
+
+  /// Shared add path — used by both the manual name/URL form and the
+  /// one-click suggested-store buttons.
+  Future<void> _addStore(String name, String url,
+      {bool fromFields = false}) async {
     if (name.isEmpty || url.isEmpty) return;
     setState(() => _busy = true);
     try {
       final r = await HubService.instance.addStore(name: name, url: url);
       if (!mounted) return;
-      _name.clear();
-      _url.clear();
+      if (fromFields) {
+        _name.clear();
+        _url.clear();
+      }
       ScaffoldMessenger.of(context)
           .showSnackBar(SnackBar(content: Text(r.message)));
       _reload();
     } catch (e) {
       if (mounted) {
         showFaiErrorSnack(context, 'store.add', e,
-            title: 'Could not add store');
+            title: AppLocalizations.of(context)!.storesManagerAddFailed);
       }
     } finally {
       if (mounted) setState(() => _busy = false);
@@ -77,7 +123,7 @@ class _ChainStoresDialogState extends State<ChainStoresDialog> {
     } catch (e) {
       if (mounted) {
         showFaiErrorSnack(context, 'store.remove', e,
-            title: 'Could not remove store');
+            title: AppLocalizations.of(context)!.storesManagerRemoveFailed);
       }
     }
   }
@@ -85,8 +131,9 @@ class _ChainStoresDialogState extends State<ChainStoresDialog> {
   @override
   Widget build(BuildContext context) {
     final theme = Theme.of(context);
+    final l = AppLocalizations.of(context)!;
     return AlertDialog(
-      title: const Text('Module stores'),
+      title: Text(l.storesManagerTitle),
       content: SizedBox(
         width: 540,
         child: Column(
@@ -94,8 +141,7 @@ class _ChainStoresDialogState extends State<ChainStoresDialog> {
           crossAxisAlignment: CrossAxisAlignment.stretch,
           children: [
             Text(
-              'The hub merges modules from every store below into one index. '
-              'Add a store index URL to make its modules installable here.',
+              l.storesManagerIntro,
               style: theme.textTheme.bodySmall
                   ?.copyWith(color: theme.colorScheme.onSurfaceVariant),
             ),
@@ -126,14 +172,14 @@ class _ChainStoresDialogState extends State<ChainStoresDialog> {
                           title: Text(s.name),
                           subtitle: Text(
                             s.url.isEmpty
-                                ? '${s.moduleCount} modules · bundled'
-                                : '${s.url}\n${s.moduleCount} modules',
+                                ? l.storesManagerBundled(s.moduleCount)
+                                : '${s.url}\n${l.storesManagerModuleCount(s.moduleCount)}',
                           ),
                           isThreeLine: s.url.isNotEmpty,
                           trailing: s.removable
                               ? IconButton(
                                   icon: const Icon(Icons.delete_outline),
-                                  tooltip: 'Remove',
+                                  tooltip: l.buttonRemove,
                                   onPressed: () => _remove(s.name),
                                 )
                               : const Icon(Icons.lock_outline, size: 16),
@@ -144,7 +190,37 @@ class _ChainStoresDialogState extends State<ChainStoresDialog> {
               ),
             ),
             const Divider(),
-            Text('Add a store', style: theme.textTheme.titleSmall),
+            // One-click curated stores — add or remove a known store
+            // (e.g. a domain app's published modules) without typing a
+            // URL. State follows the configured list above.
+            Text(l.storesManagerSuggested, style: theme.textTheme.titleSmall),
+            const SizedBox(height: ChainSpace.sm),
+            FutureBuilder<List<StoreSource>>(
+              future: _future,
+              builder: (c, snap) {
+                final stores = snap.data ?? const <StoreSource>[];
+                final configuredNameByUrl = <String, String>{
+                  for (final s in stores)
+                    if (s.url.isNotEmpty) s.url: s.name,
+                };
+                return Column(
+                  children: [
+                    for (final sg in _kSuggestedStores)
+                      _SuggestedStoreRow(
+                        store: sg,
+                        configuredName: configuredNameByUrl[sg.url],
+                        available: _reachable[sg.url],
+                        busy: _busy,
+                        onAdd: () => _addStore(sg.name, sg.url),
+                        onRemove: (name) => _remove(name),
+                      ),
+                  ],
+                );
+              },
+            ),
+            const SizedBox(height: ChainSpace.md),
+            const Divider(),
+            Text(l.storesManagerAddSection, style: theme.textTheme.titleSmall),
             const SizedBox(height: ChainSpace.sm),
             Row(
               children: [
@@ -152,8 +228,8 @@ class _ChainStoresDialogState extends State<ChainStoresDialog> {
                   flex: 2,
                   child: TextField(
                     controller: _name,
-                    decoration: const InputDecoration(
-                      labelText: 'Name',
+                    decoration: InputDecoration(
+                      labelText: l.storesManagerNameLabel,
                       isDense: true,
                     ),
                   ),
@@ -163,8 +239,8 @@ class _ChainStoresDialogState extends State<ChainStoresDialog> {
                   flex: 4,
                   child: TextField(
                     controller: _url,
-                    decoration: const InputDecoration(
-                      labelText: 'Index URL (https:// or file://)',
+                    decoration: InputDecoration(
+                      labelText: l.storesManagerUrlLabel,
                       isDense: true,
                     ),
                     onSubmitted: (_) => _add(),
@@ -178,7 +254,7 @@ class _ChainStoresDialogState extends State<ChainStoresDialog> {
       actions: [
         TextButton(
           onPressed: () => Navigator.of(context).pop(),
-          child: const Text('Close'),
+          child: Text(l.buttonClose),
         ),
         FilledButton(
           onPressed: _busy ? null : _add,
@@ -188,9 +264,150 @@ class _ChainStoresDialogState extends State<ChainStoresDialog> {
                   height: 16,
                   child: CircularProgressIndicator(strokeWidth: 2),
                 )
-              : const Text('Add store'),
+              : Text(l.storesManagerAddAction),
         ),
       ],
     );
   }
 }
+
+/// A curated, one-click store the operator can add or remove without
+/// typing a URL. The hub validates the index on add, so the entry
+/// only succeeds once its index is actually published at [url].
+class _SuggestedStore {
+  final String name;
+  final String url;
+  final String Function(AppLocalizations) describe;
+  const _SuggestedStore({
+    required this.name,
+    required this.url,
+    required this.describe,
+  });
+}
+
+/// Known stores offered as quick-adds. Keep this short and curated —
+/// it is the in-product shelf of trusted domain stores. The URL is the
+/// canonical publish location each store owner commits to (see the
+/// cross-agent handoff log for Recl∆Im's).
+final List<_SuggestedStore> _kSuggestedStores = <_SuggestedStore>[
+  _SuggestedStore(
+    name: 'Recl∆Im',
+    url: 'https://releases.chain.flemming.ai/reclaim/store.yaml',
+    describe: (l) => l.storesSuggestedReclaimDesc,
+  ),
+];
+
+/// One row in the suggested-stores shelf: icon, name, description, and
+/// a single Add/Remove button that flips based on whether the store is
+/// already configured.
+class _SuggestedStoreRow extends StatelessWidget {
+  final _SuggestedStore store;
+
+  /// The configured store's name when this suggestion is already
+  /// added (matched by URL), else null.
+  final String? configuredName;
+
+  /// Index reachability: null = still probing, true = reachable,
+  /// false = a definitive 4xx/5xx (not published yet).
+  final bool? available;
+  final bool busy;
+  final VoidCallback onAdd;
+  final ValueChanged<String> onRemove;
+
+  const _SuggestedStoreRow({
+    required this.store,
+    required this.configuredName,
+    required this.available,
+    required this.busy,
+    required this.onAdd,
+    required this.onRemove,
+  });
+
+  @override
+  Widget build(BuildContext context) {
+    final theme = Theme.of(context);
+    final l = AppLocalizations.of(context)!;
+    final added = configuredName != null;
+    // Not-yet-published: a definitive bad response and not already
+    // configured. Show a muted "not available yet" chip instead of an
+    // Add button that would only fail on click.
+    final notPublished = !added && available == false;
+    final probing = !added && available == null;
+    return Padding(
+      padding: const EdgeInsets.symmetric(vertical: 2),
+      child: Row(
+        children: [
+          Icon(
+            Icons.storefront_outlined,
+            size: 18,
+            color: theme.colorScheme.primary,
+          ),
+          const SizedBox(width: ChainSpace.sm),
+          Expanded(
+            child: Column(
+              crossAxisAlignment: CrossAxisAlignment.start,
+              children: [
+                Text(
+                  store.name,
+                  style: theme.textTheme.bodyMedium
+                      ?.copyWith(fontWeight: FontWeight.w600),
+                ),
+                Text(
+                  store.describe(l),
+                  style: theme.textTheme.bodySmall
+                      ?.copyWith(color: theme.colorScheme.onSurfaceVariant),
+                ),
+              ],
+            ),
+          ),
+          const SizedBox(width: ChainSpace.sm),
+          if (added)
+            OutlinedButton.icon(
+              icon: const Icon(Icons.check, size: 14),
+              label: Text(l.buttonRemove),
+              onPressed: busy ? null : () => onRemove(configuredName!),
+              style: OutlinedButton.styleFrom(
+                visualDensity: VisualDensity.compact,
+                foregroundColor: ChainColors.success,
+              ),
+            )
+          else if (probing)
+            const SizedBox(
+              width: 16,
+              height: 16,
+              child: CircularProgressIndicator(strokeWidth: 2),
+            )
+          else if (notPublished)
+            Tooltip(
+              message: l.storesManagerNotAvailableHint,
+              child: Row(
+                mainAxisSize: MainAxisSize.min,
+                children: [
+                  Icon(
+                    Icons.schedule_outlined,
+                    size: 14,
+                    color: theme.colorScheme.onSurfaceVariant,
+                  ),
+                  const SizedBox(width: 4),
+                  Text(
+                    l.storesManagerNotAvailable,
+                    style: theme.textTheme.bodySmall
+                        ?.copyWith(color: theme.colorScheme.onSurfaceVariant),
+                  ),
+                ],
+              ),
+            )
+          else
+            FilledButton.tonalIcon(
+              icon: const Icon(Icons.add, size: 14),
+              label: Text(l.storesManagerAddShort),
+              onPressed: busy ? null : onAdd,
+              style: FilledButton.styleFrom(
+                visualDensity: VisualDensity.compact,
+              ),
+            ),
+        ],
+      ),
+    );
+  }
+}