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_de.dart

@@ -261,7 +261,7 @@ class AppLocalizationsDe extends AppLocalizations {
 
   @override
   String get sidebarChannelTooltip =>
-      'Aktiver Kanal — klicken um in Einstellungen (⌘;) zu wechseln.\nproduction = stabil · beta = Vorabversion · dev = laufend · local = Arbeitsumgebung';
+      'Aktiver Kanal — klicken zum Wechseln.\nproduction = stabil · beta = Vorabversion · dev = laufend · local = Arbeitsumgebung';
 
   @override
   String get buttonCancel => 'Abbrechen';
@@ -771,6 +771,61 @@ class AppLocalizationsDe extends AppLocalizations {
   @override
   String get storeReloadTooltip => 'Aktualisieren';
 
+  @override
+  String get storesManagerButton => 'Store hinzufügen';
+
+  @override
+  String get storesManagerTitle => 'Module-Stores';
+
+  @override
+  String get storesManagerIntro =>
+      'Der Hub führt die Module aller Stores unten zu einem Index zusammen. Füge die Index-URL eines Stores hinzu, damit seine Module hier installierbar werden.';
+
+  @override
+  String get storesManagerAddSection => 'Store hinzufügen';
+
+  @override
+  String get storesManagerNameLabel => 'Name';
+
+  @override
+  String get storesManagerUrlLabel => 'Index-URL (https:// oder file://)';
+
+  @override
+  String get storesManagerAddAction => 'Hinzufügen';
+
+  @override
+  String storesManagerBundled(int count) {
+    return '$count Module · gebündelt';
+  }
+
+  @override
+  String storesManagerModuleCount(int count) {
+    return '$count Module';
+  }
+
+  @override
+  String get storesManagerAddFailed => 'Store konnte nicht hinzugefügt werden';
+
+  @override
+  String get storesManagerRemoveFailed => 'Store konnte nicht entfernt werden';
+
+  @override
+  String get storesManagerSuggested => 'Vorgeschlagene Stores';
+
+  @override
+  String get storesManagerAddShort => 'Hinzufügen';
+
+  @override
+  String get storesManagerNotAvailable => 'Noch nicht verfügbar';
+
+  @override
+  String get storesManagerNotAvailableHint =>
+      'Der Anbieter hat diesen Store-Index noch nicht veröffentlicht. Sobald er das tut, ist er installierbar.';
+
+  @override
+  String get storesSuggestedReclaimDesc =>
+      'Recl∆Im — Module für Rechts- und Pflichten-Reform-Mapping';
+
   @override
   String get storeTodayBadge => 'HEUTE';
 
@@ -1712,7 +1767,16 @@ class AppLocalizationsDe extends AppLocalizations {
   String get approvalsPillExpired => 'abgelaufen';
 
   @override
-  String get approvalsPayloadPreview => 'PAYLOAD-VORSCHAU';
+  String get approvalsPayloadPreview => 'DIESE DATEN WERDEN FREIGEGEBEN';
+
+  @override
+  String get approvalsRequestFallback =>
+      'Freigabe für diesen Schritt erforderlich';
+
+  @override
+  String approvalsFlowStepMeta(String flow, String step) {
+    return 'Flow: $flow · Schritt: $step';
+  }
 
   @override
   String get approvalsApproveButton => 'Freigeben';