refactor(auto-update): retire per-stack gate, drive auto-update from schedules only (#1233)

* refactor(auto-update): retire per-stack gate, drive auto-update from schedules only

The per-stack Auto-update toggle in the stack sidebar context menu wrote a
gate row to `stack_auto_update_settings`, but actual updates only ran when a
`scheduled_tasks` row with `action='update'` fired. On a fresh install the
toggle was inert: detection ran every 6h, nothing was applied.

The same context menu already exposes `Schedule task`, which opens
ScheduledOperationsView pre-filled for the stack where the user can pick
`Auto-update Stack` and any cron. Keeping the toggle alongside that flow
duplicated the same action and turned the gate table into a parallel store
of "is a covering schedule active" derivable from `scheduled_tasks` itself.

Drop the gate model entirely:
- Backend: remove the `stack_auto_update_settings` table and its four
  accessors, the three routes under /api/stacks/*/auto-update, the per-stack
  skip in /api/auto-update/execute and SchedulerService.executeUpdate's
  fleet branch, and the clearStackAutoUpdateSetting call on stack delete.
  Dashboard `autoUpdate` count derives from scheduled_tasks (action='update'
  rows pinned to the node, total/enabled split).
- Frontend: drop the Auto-update entry from the sidebar context menu and its
  optimistic toggle plumbing. Drop autoUpdateSettings state, the
  /stacks/auto-update-settings fetch, and the auto-update-settings-changed
  WebSocket branch. Slim useSidebarActivitySummary (just nextRunAt; no
  enabled/total counts). AutoUpdateReadinessView's per-card autoUpdateEnabled
  now means "a covering enabled action='update' schedule exists" (per-stack
  row or fleet row on this node, earliest next_run_at wins, per-stack row
  wins on ties), with the gate-fetch removed.
- New: scheduledTasksRouter broadcasts scope: 'scheduled-tasks' on POST,
  PUT, PATCH /toggle, and DELETE so useConfigurationStatus and
  useNextAutoUpdateRun refetch under the 250ms debounce instead of waiting
  for the 60s poll. The broadcast is wrapped so a broken subscriber socket
  cannot turn a successful mutation into a 500.
- Docs: rewrite the "Per-stack control" section of auto-update-policies.mdx
  to describe the schedule-based model; update the matching troubleshooting
  entry. The misleading fleet-update help text in ScheduledOperationsView
  is corrected to reflect that every stack on the node is covered.

Tier parity: the surviving auto-update path (Schedule task -> Auto-update
Stack / All Stacks) is gated `requirePaid + requireAdmin` backend and
`isPaid + isAdmin` frontend, matching the gate the deleted routes carried.
The pre-commit grep returns no tier-related diff outside this PR's scope.

No data migration is provided: greenfield rules apply, and the leftover
table on already-shipped instances is harmless because no code reads or
writes it after this PR.

* docs: sweep remaining references to the per-stack auto-update toggle

The previous commit retired the per-stack Auto-update gate in favor of
configuring auto-update purely through scheduled tasks. This commit
removes the now-stale mentions of that toggle across the operator docs:

- docs/features/sidebar.mdx: drop the Auto-update entry from the Inspect
  group description, the matching screenshot alt-text, and the Skipper
  Note that listed it. Schedule task now carries the cross-link to
  Auto-Update Policies.
- docs/features/stack-management.mdx: drop the Auto-update list item;
  refresh the Schedule task entry to mention the Auto-update Stack action.
- docs/features/dashboard.mdx: rename the Configuration Status row from
  "Auto-update stacks" to "Auto-update schedules" with the new value
  shape, and rewrite the troubleshooting accordion to describe the
  scheduled-tasks invalidation path.
- docs/features/scheduled-operations.mdx: rewrite the Auto-update All
  Stacks row and helper text to reflect that every stack on the node is
  covered (no per-stack opt-out from this surface anymore).
- docs/features/multi-node.mdx: rewrite the Updates column definition to
  derive the Auto/Off flag from enabled Auto-update Stack / Auto-update
  All Stacks schedules instead of the removed per-stack policy.

The auto-update-policies.mdx rewrite in the previous commit already
covered the main reference page. The sidebar-context-menu.png screenshot
will be refreshed on release once the new menu is live in production;
the alt text is updated in this commit so it accurately describes the
shipping state.

No website edits needed: the Auto-Update Policies feature card description
("Schedule automatic image pulls and redeployments per stack on your own
cadence") and the feature matrix labels ("Auto-update stack schedule",
"Auto-update all stacks schedule") remain accurate under the new model.

* fix(stacks): drop orphaned requireAdmin import after auto-update route removal

CI's backend lint step flagged this PR's earlier deletion of the three
/api/stacks/*/auto-update routes: those handlers were the only callers of
`requireAdmin` inside routes/stacks.ts, leaving the named import on line 15
unreferenced. `requirePaid` and `effectiveTier` from the same line are still
in use elsewhere in the file and stay.

tsc --noEmit does not flag unused named imports; ESLint's no-unused-vars
does. Local backend lint reproduces and now reports 0 errors against the
existing 334-warning baseline.

backend/src/__tests__/scheduler-service.test.ts

@@ -21,7 +21,6 @@ const {
   mockGetProxyTarget,
   mockIsTrivyAvailable,
   mockScanAllNodeImages,
-  mockGetStackAutoUpdateSettingsForNode,
   mockDeleteScheduledTask,
   mockGetMatchingPolicy,
   mockRunCommand,
@@ -62,7 +61,6 @@ const {
     severity: { critical: 0, high: 0, medium: 0, low: 0, unknown: 0 },
     violations: [],
   }),
-  mockGetStackAutoUpdateSettingsForNode: vi.fn().mockReturnValue({}),
   mockDeleteScheduledTask: vi.fn(),
   mockGetMatchingPolicy: vi.fn().mockReturnValue(null),
   mockRunCommand: vi.fn().mockResolvedValue(undefined),
@@ -86,7 +84,6 @@ vi.mock('../services/DatabaseService', () => ({
       clearStackUpdateStatus: mockClearStackUpdateStatus,
       markStaleRunsAsFailed: mockMarkStaleRunsAsFailed,
       deleteOldScans: mockDeleteOldScans,
-      getStackAutoUpdateSettingsForNode: mockGetStackAutoUpdateSettingsForNode,
       deleteScheduledTask: mockDeleteScheduledTask,
       getMatchingPolicy: mockGetMatchingPolicy,
     }),
@@ -790,7 +787,7 @@ describe('SchedulerService - executeUpdate', () => {
     expect(svc.isTaskRunning(999)).toBe(false);
   });
 
-  it('fleet target updates all stacks whose policy allows it', async () => {
+  it('fleet target updates every stack discovered on the node', async () => {
     mockGetScheduledTask.mockReturnValue({
       id: 87,
       name: 'fleet-update',
@@ -804,45 +801,13 @@ describe('SchedulerService - executeUpdate', () => {
       last_status: null,
     });
     mockGetStacks.mockResolvedValue(['app1', 'app2', 'app3']);
-    // app2 explicitly disabled; app1 and app3 default to enabled
-    mockGetStackAutoUpdateSettingsForNode.mockReturnValue({ app2: false });
     mockGetContainersByStack.mockResolvedValue([{ Id: 'c1', Image: 'nginx:latest' }]);
     mockCheckImage.mockResolvedValue({ hasUpdate: true });
 
     const svc = SchedulerService.getInstance();
     await svc.triggerTask(87);
 
-    // Only app1 and app3 should be updated
-    expect(mockUpdateStack).toHaveBeenCalledTimes(2);
-    expect(mockUpdateScheduledTaskRun).toHaveBeenCalledWith(
-      1,
-      expect.objectContaining({
-        status: 'success',
-        output: expect.stringContaining('auto-updates disabled; skipped'),
-      })
-    );
-  });
-
-  it('fleet target with zero eligible stacks records success', async () => {
-    mockGetScheduledTask.mockReturnValue({
-      id: 88,
-      name: 'fleet-update-all-off',
-      action: 'update',
-      target_type: 'fleet',
-      cron_expression: '0 4 * * *',
-      enabled: true,
-      target_id: null,
-      node_id: 1,
-      created_by: 'admin',
-      last_status: null,
-    });
-    mockGetStacks.mockResolvedValue(['app1', 'app2']);
-    mockGetStackAutoUpdateSettingsForNode.mockReturnValue({ app1: false, app2: false });
-
-    const svc = SchedulerService.getInstance();
-    await svc.triggerTask(88);
-
-    expect(mockUpdateStack).not.toHaveBeenCalled();
+    expect(mockUpdateStack).toHaveBeenCalledTimes(3);
     expect(mockUpdateScheduledTaskRun).toHaveBeenCalledWith(
       1,
       expect.objectContaining({ status: 'success' })