feat(auto-update): per-stack auto-update enable/disable toggle (#771)

* feat(auto-update): add per-stack auto-update enable/disable toggle

Paid users (Skipper and Admiral) can now opt individual stacks out of
scheduled auto-updates from the stack context menu without disabling
the global feature.

- Add stack_auto_update_settings table (node_id, stack_name) with
  default enabled=true; four typed DatabaseService accessors with
  parameterized queries.
- Add GET /stacks/auto-update-settings, GET /stacks/:name/auto-update,
  and PUT /stacks/:name/auto-update (requirePaid + requireAdmin).
  PUT broadcasts state-invalidate with action auto-update-settings-changed
  so all open tabs refresh immediately.
- Stack DELETE clears the auto-update setting row alongside stack_update_status.
- autoUpdateRouter /execute skips disabled stacks before any registry
  call; skip is recorded in the results array. Manual Update actions
  are not affected.
- Add Auto-update: Enabled/Disabled toggle in the stack inspect group
  (paid tiers only, hidden for Community, consistent with Auto-Heal).
  Toggle uses optimistic update with revert-on-error toast.
- AutoUpdateReadinessView shows an Auto: Off pill and disables the
  Apply now button for stacks with auto-updates off. Detection still
  runs so the readiness card remains visible.
- Add 21 backend Vitest tests covering DB round-trips, endpoint auth
  and tier gates, execute skip for both wildcard and named targets.
  Add 3 frontend hook tests for toggle visibility and callback behavior.

* docs(auto-update): document per-stack auto-update control

Add a Per-stack control section to the auto-update readiness page
explaining how to disable and re-enable auto-updates for individual
stacks, what disabling means (scheduled apply skipped; detection still
runs; manual update unaffected), and a troubleshooting entry for
scheduled runs not applying to a specific stack.

frontend/src/hooks/useStackMenuItems.tsx

@@ -3,6 +3,7 @@ import {
   Activity,
   ArrowUpRight,
   BellRing,
+  CircleSlash,
   Download,
   Pin,
   PinOff,
@@ -20,7 +21,7 @@ export function useStackMenuItems(_file: string, ctx: StackMenuCtx): MenuGroup[]
     stackStatus, hasPort, isBusy, isPaid, canDelete, isPinned, labels,
     openAlertSheet, openAutoHeal, checkUpdates, openStackApp,
     deploy, stop, restart, update, remove, pin, unpin, toggleLabel,
-    menuVisibility,
+    menuVisibility, autoUpdateEnabled, setAutoUpdateEnabled,
   } = ctx;
   const { showDeploy, showStop, showRestart, showUpdate } = menuVisibility;
 
@@ -32,6 +33,12 @@ export function useStackMenuItems(_file: string, ctx: StackMenuCtx): MenuGroup[]
     ];
     if (isPaid) {
       inspect.push({ id: 'auto-heal', label: 'Auto-Heal', icon: Activity, shortcut: 'H', onSelect: openAutoHeal });
+      inspect.push({
+        id: 'auto-update',
+        label: autoUpdateEnabled ? 'Auto-update: Enabled' : 'Auto-update: Disabled',
+        icon: autoUpdateEnabled ? RefreshCw : CircleSlash,
+        onSelect: () => setAutoUpdateEnabled(!autoUpdateEnabled),
+      });
     }
     inspect.push({ id: 'check-updates', label: 'Check updates', icon: RefreshCw, shortcut: 'U', onSelect: checkUpdates });
     if (stackStatus === 'running' && hasPort) {
@@ -80,6 +87,7 @@ export function useStackMenuItems(_file: string, ctx: StackMenuCtx): MenuGroup[]
   }, [
     stackStatus, hasPort, isBusy, isPaid, canDelete, isPinned, labels,
     showDeploy, showStop, showRestart, showUpdate,
+    autoUpdateEnabled, setAutoUpdateEnabled,
     openAlertSheet, openAutoHeal, checkUpdates, openStackApp,
     deploy, stop, restart, update, remove, pin, unpin, toggleLabel,
   ]);