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_de.arb

@@ -81,7 +81,7 @@
   "connectionStartHub": "Hub starten",
   "connectionTapToStart": "antippen zum Starten",
   "sidebarSettingsTooltip": "Einstellungen (⌘;)",
-  "sidebarChannelTooltip": "Aktiver Kanal — klicken um in Einstellungen (⌘;) zu wechseln.\nproduction = stabil · beta = Vorabversion · dev = laufend · local = Arbeitsumgebung",
+  "sidebarChannelTooltip": "Aktiver Kanal — klicken zum Wechseln.\nproduction = stabil · beta = Vorabversion · dev = laufend · local = Arbeitsumgebung",
   "buttonCancel": "Abbrechen",
   "buttonSave": "Speichern",
   "buttonClose": "Schließen",
@@ -319,6 +319,22 @@
     }
   },
   "storeReloadTooltip": "Aktualisieren",
+  "storesManagerButton": "Store hinzufügen",
+  "storesManagerTitle": "Module-Stores",
+  "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.",
+  "storesManagerAddSection": "Store hinzufügen",
+  "storesManagerNameLabel": "Name",
+  "storesManagerUrlLabel": "Index-URL (https:// oder file://)",
+  "storesManagerAddAction": "Hinzufügen",
+  "storesManagerBundled": "{count} Module · gebündelt",
+  "storesManagerModuleCount": "{count} Module",
+  "storesManagerAddFailed": "Store konnte nicht hinzugefügt werden",
+  "storesManagerRemoveFailed": "Store konnte nicht entfernt werden",
+  "storesManagerSuggested": "Vorgeschlagene Stores",
+  "storesManagerAddShort": "Hinzufügen",
+  "storesManagerNotAvailable": "Noch nicht verfügbar",
+  "storesManagerNotAvailableHint": "Der Anbieter hat diesen Store-Index noch nicht veröffentlicht. Sobald er das tut, ist er installierbar.",
+  "storesSuggestedReclaimDesc": "Recl∆Im — Module für Rechts- und Pflichten-Reform-Mapping",
   "storeTodayBadge": "HEUTE",
   "storeTodayDeck": "Von der Ch∆In-Redaktion",
   "storeTodayDismissTooltip": "Für diese Sitzung ausblenden",
@@ -998,7 +1014,9 @@
   "approvalsPillApproved": "freigegeben",
   "approvalsPillRejected": "abgelehnt",
   "approvalsPillExpired": "abgelaufen",
-  "approvalsPayloadPreview": "PAYLOAD-VORSCHAU",
+  "approvalsPayloadPreview": "DIESE DATEN WERDEN FREIGEGEBEN",
+  "approvalsRequestFallback": "Freigabe für diesen Schritt erforderlich",
+  "approvalsFlowStepMeta": "Flow: {flow} · Schritt: {step}",
   "approvalsApproveButton": "Freigeben",
   "approvalsRejectButton": "Ablehnen",
   "approvalsRejectDialogTitle": "Freigabe ablehnen",