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/l10n/app_localizations_en.dart

@@ -260,7 +260,7 @@ class AppLocalizationsEn extends AppLocalizations {
 
   @override
   String get sidebarChannelTooltip =>
-      'Active channel — click to switch in Settings (⌘;).\nproduction = stable · beta = pre-release · dev = rolling · local = workspace';
+      'Active channel — click to switch.\nproduction = stable · beta = pre-release · dev = rolling · local = workspace';
 
   @override
   String get buttonCancel => 'Cancel';
@@ -789,6 +789,61 @@ class AppLocalizationsEn extends AppLocalizations {
   @override
   String get storeReloadTooltip => 'Reload';
 
+  @override
+  String get storesManagerButton => 'Add store';
+
+  @override
+  String get storesManagerTitle => 'Module stores';
+
+  @override
+  String get storesManagerIntro =>
+      'The hub merges the modules from every store below into one index. Add a store\'s index URL to make its modules installable here.';
+
+  @override
+  String get storesManagerAddSection => 'Add a store';
+
+  @override
+  String get storesManagerNameLabel => 'Name';
+
+  @override
+  String get storesManagerUrlLabel => 'Index URL (https:// or file://)';
+
+  @override
+  String get storesManagerAddAction => 'Add store';
+
+  @override
+  String storesManagerBundled(int count) {
+    return '$count modules · bundled';
+  }
+
+  @override
+  String storesManagerModuleCount(int count) {
+    return '$count modules';
+  }
+
+  @override
+  String get storesManagerAddFailed => 'Could not add store';
+
+  @override
+  String get storesManagerRemoveFailed => 'Could not remove store';
+
+  @override
+  String get storesManagerSuggested => 'Suggested stores';
+
+  @override
+  String get storesManagerAddShort => 'Add';
+
+  @override
+  String get storesManagerNotAvailable => 'Not available yet';
+
+  @override
+  String get storesManagerNotAvailableHint =>
+      'The provider hasn\'t published this store index yet. It will become installable once they do.';
+
+  @override
+  String get storesSuggestedReclaimDesc =>
+      'Recl∆Im — modules for law & duty reform-mapping';
+
   @override
   String get storeTodayBadge => 'TODAY';
 
@@ -1722,7 +1777,15 @@ class AppLocalizationsEn extends AppLocalizations {
   String get approvalsPillExpired => 'expired';
 
   @override
-  String get approvalsPayloadPreview => 'PAYLOAD PREVIEW';
+  String get approvalsPayloadPreview => 'DATA TO BE RELEASED';
+
+  @override
+  String get approvalsRequestFallback => 'Approval required for this step';
+
+  @override
+  String approvalsFlowStepMeta(String flow, String step) {
+    return 'Flow: $flow · Step: $step';
+  }
 
   @override
   String get approvalsApproveButton => 'Approve';