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.

frontend/src/components/EditorLayout.tsx

@@ -1,4 +1,4 @@
-import { useCallback, useEffect, useMemo, useRef } from 'react';
+import { useCallback, useEffect, useRef } from 'react';
 import { Button } from './ui/button';
 import { Plus } from 'lucide-react';
 import { UserProfileDropdown } from './UserProfileDropdown';
@@ -32,7 +32,7 @@ import { useDeployFeedback } from '@/context/DeployFeedbackContext';
 import { useTrivyStatus } from '@/hooks/useTrivyStatus';
 import { StackSidebar } from '@/components/sidebar/StackSidebar';
 import type { StackRowStatus } from '@/components/sidebar/stack-status-utils';
-import { useSidebarActivitySummary, countEnabledAutoUpdates } from '@/components/sidebar/useSidebarActivitySummary';
+import { useSidebarActivitySummary } from '@/components/sidebar/useSidebarActivitySummary';
 import { useNextAutoUpdateRun } from '@/components/sidebar/useNextAutoUpdateRun';
 import { usePanelSessionStartedAt } from '@/components/sidebar/usePanelSessionStartedAt';
 import type { SidebarActivityAction } from '@/components/sidebar/SidebarActivityTicker';
@@ -68,7 +68,6 @@ export default function EditorLayout() {
 
   const stackListState = useStackListState();
   const {
-    files,
     selectedFile,
     isLoading,
     stackActions: stackActionMap,
@@ -76,7 +75,6 @@ export default function EditorLayout() {
     searchQuery, setSearchQuery,
     stackStatuses,
     stackLabelMap,
-    autoUpdateSettings,
     filterChip, setFilterChip,
     bulkMode,
     selectedFiles,
@@ -85,7 +83,6 @@ export default function EditorLayout() {
     remoteResults,
     isStackBusy,
     refreshStacks,
-    fetchAutoUpdateSettings,
     handleScanStacks,
     scheduleStateInvalidateRefresh,
     toggleBulkMode, toggleSelect, clearSelection, handleBulkAction,
@@ -147,7 +144,6 @@ export default function EditorLayout() {
   } = useNotifications({
     nodes,
     onStateInvalidate: scheduleStateInvalidateRefresh,
-    onAutoUpdateChange: fetchAutoUpdateSettings,
     onImageUpdatesChange: fetchImageUpdates,
   });
 
@@ -190,19 +186,12 @@ export default function EditorLayout() {
 
   const panelStartedAt = usePanelSessionStartedAt(panelState);
 
-  const autoUpdateEnabledCount = useMemo(
-    () => countEnabledAutoUpdates(files, autoUpdateSettings),
-    [files, autoUpdateSettings],
-  );
-
   const nextAutoUpdateRunAt = useNextAutoUpdateRun();
   const activitySummary = useSidebarActivitySummary({
     notifications,
     tickerConnected,
     panelState,
     panelStartedAt,
-    autoUpdateEnabledCount,
-    totalStackCount: files.length,
     nextAutoUpdateRunAt,
   });
 
@@ -292,7 +281,6 @@ export default function EditorLayout() {
     }
 
     refreshStacks();
-    fetchAutoUpdateSettings();
     void stackActions.refreshGitSourcePending();
   }, [activeNode?.id]); // eslint-disable-line react-hooks/exhaustive-deps