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_en.arb

@@ -84,7 +84,7 @@
   "connectionStartHub": "Start hub",
   "connectionTapToStart": "tap to start",
   "sidebarSettingsTooltip": "Settings (⌘;)",
-  "sidebarChannelTooltip": "Active channel — click to switch in Settings (⌘;).\nproduction = stable · beta = pre-release · dev = rolling · local = workspace",
+  "sidebarChannelTooltip": "Active channel — click to switch.\nproduction = stable · beta = pre-release · dev = rolling · local = workspace",
   "buttonCancel": "Cancel",
   "buttonSave": "Save",
   "buttonClose": "Close",
@@ -322,6 +322,32 @@
     }
   },
   "storeReloadTooltip": "Reload",
+  "storesManagerButton": "Add store",
+  "storesManagerTitle": "Module stores",
+  "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.",
+  "storesManagerAddSection": "Add a store",
+  "storesManagerNameLabel": "Name",
+  "storesManagerUrlLabel": "Index URL (https:// or file://)",
+  "storesManagerAddAction": "Add store",
+  "storesManagerBundled": "{count} modules · bundled",
+  "@storesManagerBundled": {
+    "placeholders": {
+      "count": { "type": "int" }
+    }
+  },
+  "storesManagerModuleCount": "{count} modules",
+  "@storesManagerModuleCount": {
+    "placeholders": {
+      "count": { "type": "int" }
+    }
+  },
+  "storesManagerAddFailed": "Could not add store",
+  "storesManagerRemoveFailed": "Could not remove store",
+  "storesManagerSuggested": "Suggested stores",
+  "storesManagerAddShort": "Add",
+  "storesManagerNotAvailable": "Not available yet",
+  "storesManagerNotAvailableHint": "The provider hasn't published this store index yet. It will become installable once they do.",
+  "storesSuggestedReclaimDesc": "Recl∆Im — modules for law & duty reform-mapping",
   "storeTodayBadge": "TODAY",
   "storeTodayDeck": "From the Ch∆In editor",
   "storeTodayDismissTooltip": "Hide for this session",
@@ -1001,7 +1027,15 @@
   "approvalsPillApproved": "approved",
   "approvalsPillRejected": "rejected",
   "approvalsPillExpired": "expired",
-  "approvalsPayloadPreview": "PAYLOAD PREVIEW",
+  "approvalsPayloadPreview": "DATA TO BE RELEASED",
+  "approvalsRequestFallback": "Approval required for this step",
+  "approvalsFlowStepMeta": "Flow: {flow} · Step: {step}",
+  "@approvalsFlowStepMeta": {
+    "placeholders": {
+      "flow": { "type": "String" },
+      "step": { "type": "String" }
+    }
+  },
   "approvalsApproveButton": "Approve",
   "approvalsRejectButton": "Reject",
   "approvalsRejectDialogTitle": "Reject approval",