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/pages/welcome.dart

@@ -1003,18 +1003,37 @@ class _DocsRow extends StatelessWidget {
                 ],
               );
             }
-            final cardWidth = (constraints.maxWidth - ChainSpace.md) / 2;
-            return Wrap(
-              spacing: ChainSpace.md,
-              runSpacing: ChainSpace.md,
-              children: [
-                for (final d in _kDocs)
-                  SizedBox(
-                    width: cardWidth,
-                    child: _DocCard(entry: d),
+            // Pair the cards into equal-height rows: IntrinsicHeight
+            // + stretch makes the two cards in a row match height
+            // instead of the Wrap's ragged tops (their blurbs differ
+            // in length, especially across locales). An odd trailing
+            // card spans the full width so it reads as intentional
+            // rather than a lonely half-box with dead space beside it.
+            final rows = <Widget>[];
+            for (var i = 0; i < _kDocs.length; i += 2) {
+              if (rows.isNotEmpty) {
+                rows.add(const SizedBox(height: ChainSpace.md));
+              }
+              final left = _kDocs[i];
+              final right = i + 1 < _kDocs.length ? _kDocs[i + 1] : null;
+              if (right == null) {
+                rows.add(_DocCard(entry: left));
+              } else {
+                rows.add(
+                  IntrinsicHeight(
+                    child: Row(
+                      crossAxisAlignment: CrossAxisAlignment.stretch,
+                      children: [
+                        Expanded(child: _DocCard(entry: left)),
+                        const SizedBox(width: ChainSpace.md),
+                        Expanded(child: _DocCard(entry: right)),
+                      ],
+                    ),
                   ),
-              ],
-            );
+                );
+              }
+            }
+            return Column(children: rows);
           },
         ),
       ],