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/sidebar/useSidebarActivitySummary.ts

@@ -9,7 +9,7 @@ const RECENT_WINDOW_SECS = 60 * 60;
 export type SidebarActivitySummary =
   | { kind: 'active-op'; stackName: string; action: ActionVerb; startedAt: number }
   | { kind: 'failure'; notif: NotificationItem }
-  | { kind: 'automation'; enabledCount: number; totalCount: number; nextRunAt: number }
+  | { kind: 'automation'; nextRunAt: number }
   | { kind: 'recent-event'; notif: NotificationItem }
   | { kind: 'quiet-live' }
   | { kind: 'disconnected' };
@@ -19,9 +19,6 @@ interface SummaryInputs {
   tickerConnected: boolean;
   panelState: DeployPanelState;
   panelStartedAt: number | null;
-  /** Pre-aggregated by the caller so the memo dep list stays scalar; see EditorLayout. */
-  autoUpdateEnabledCount: number;
-  totalStackCount: number;
   nextAutoUpdateRunAt: number | null;
 }
 
@@ -54,7 +51,7 @@ function findRecent(notifications: NotificationItem[], nowSecs: number): Notific
  *   1. active-op:    a deploy panel is preparing/streaming
  *   2. failure:      newest unread stack-scoped error in the last 24h
  *   3. recent-event: newest non-error stack notification in the last hour
- *   4. automation:   auto-update is enabled and a next run is scheduled
+ *   4. automation:   a next auto-update run is scheduled
  *   5. disconnected: notification WebSocket is down
  *   6. quiet-live:   nothing else to surface
  *
@@ -64,7 +61,7 @@ function findRecent(notifications: NotificationItem[], nowSecs: number): Notific
  * follow the same order; if you change the cascade, update both.
  */
 function deriveSummary(inputs: SummaryInputs, nowSecs: number): SidebarActivitySummary {
-  const { panelState, panelStartedAt, notifications, autoUpdateEnabledCount, totalStackCount, nextAutoUpdateRunAt, tickerConnected } = inputs;
+  const { panelState, panelStartedAt, notifications, nextAutoUpdateRunAt, tickerConnected } = inputs;
 
   if (panelState.isOpen && (panelState.status === 'preparing' || panelState.status === 'streaming') && panelStartedAt !== null) {
     return { kind: 'active-op', stackName: panelState.stackName, action: panelState.action, startedAt: panelStartedAt };
@@ -77,8 +74,8 @@ function deriveSummary(inputs: SummaryInputs, nowSecs: number): SidebarActivityS
   }
 
   const recent = findRecent(notifications, nowSecs);
-  if (!recent && autoUpdateEnabledCount > 0 && nextAutoUpdateRunAt !== null) {
-    return { kind: 'automation', enabledCount: autoUpdateEnabledCount, totalCount: totalStackCount, nextRunAt: nextAutoUpdateRunAt };
+  if (!recent && nextAutoUpdateRunAt !== null) {
+    return { kind: 'automation', nextRunAt: nextAutoUpdateRunAt };
   }
 
   if (recent) {
@@ -111,23 +108,10 @@ export function useSidebarActivitySummary(inputs: SummaryInputs): SidebarActivit
       inputs.panelState.action,
       inputs.panelState.status,
       inputs.panelStartedAt,
-      inputs.autoUpdateEnabledCount,
-      inputs.totalStackCount,
       inputs.nextAutoUpdateRunAt,
     ],
   );
 }
 
-/**
- * Count stacks with auto-update enabled. Backend defaults missing rows to
- * enabled (DatabaseService.getStackAutoUpdateSettingsForNode); callers must
- * NOT treat absence as disabled.
- */
-export function countEnabledAutoUpdates(files: string[], settings: Record<string, boolean>): number {
-  let n = 0;
-  for (const f of files) if (settings[f] ?? true) n++;
-  return n;
-}
-
 // Exported for unit tests so we don't need to spin up a renderer to validate cascade logic.
 export const __testing = { deriveSummary };