feat(dashboard): replace 24h charts with Configuration Status and Recent Activity (#785)

* feat(dashboard): replace 24h charts with Configuration Status and Recent Activity

The 24-hour CPU/Memory area charts summed per-container metrics normalized
to each container's CPU quota, producing numbers that bore no honest
relationship to host load. The live ResourceGauges strip already shows
accurate host-level stats, making the historical charts both inaccurate
and redundant.

This commit replaces that row with two side-by-side cards:

- **Configuration Status**: aggregates every toggleable feature on the
  active node (notification agents, alert rules, routing rules, auto-heal,
  auto-update, webhooks, scheduled tasks, MFA, SSO, vulnerability scanning,
  cloud backup, and alert thresholds) into a single at-a-glance card.
  Tier-locked rows display an upgrade indicator instead of a value.
  Each row is clickable and navigates to the relevant settings section.
  Data refreshes every 60 s and immediately on state-invalidate events.

- **Recent Activity**: lists the ten most recent notification-history events
  for the active node (deployments, image updates, auto-heal actions, scan
  findings, cloud backup events, system notices) with category icons and
  relative timestamps. Refreshes every 30 s.

New backend endpoints:
- GET /api/dashboard/configuration - per-node feature status with locked/
  requiredTier markers so the frontend renders upgrade chips without extra
  calls. The endpoint sits after authGate and before the remote proxy so
  remote-node requests are transparently forwarded.
- GET /api/dashboard/recent-activity?limit=N - thin wrapper over
  DatabaseService.getNotificationHistory.
- GET /api/fleet/configuration - fleet-wide fan-out using the same
  Promise.allSettled dead-node-tolerant pattern as /fleet/overview.
  Exposed as the new "Status" tab on the Fleet page (after Snapshots).

Shared utilities:
- visibilityInterval and formatCount extracted to frontend/src/lib/utils.ts
  so the three polling hooks and two components share a single copy.

* docs(dashboard): fix stale alt text referencing removed historical charts

frontend/src/components/EditorLayout.tsx

@@ -6,6 +6,7 @@ import TerminalComponent from './Terminal';
 import ErrorBoundary from './ErrorBoundary';
 import HomeDashboard from './HomeDashboard';
 import type { NotificationItem } from './dashboard/types';
+import type { SectionId } from './settings/types';
 import BashExecModal from './BashExecModal';
 import HostConsole from './HostConsole';
 import { AdmiralGate } from './AdmiralGate';
@@ -360,7 +361,7 @@ export default function EditorLayout() {
   const [notifications, setNotifications] = useState<NotificationItem[]>([]);
   const [tickerConnected, setTickerConnected] = useState(false);
   const [settingsModalOpen, setSettingsModalOpen] = useState(false);
-  const [settingsInitialSection, setSettingsInitialSection] = useState<'account' | 'labels' | 'nodes'>('account');
+  const [settingsInitialSection, setSettingsInitialSection] = useState<SectionId>('account');
   const [alertSheetOpen, setAlertSheetOpen] = useState(false);
   const [alertSheetStack, setAlertSheetStack] = useState('');
   const [autoHealStackName, setAutoHealStackName] = useState<string | null>(null);
@@ -2922,6 +2923,7 @@ export default function EditorLayout() {
               onNavigateToStack={(stackFile) => { loadFile(stackFile); }}
               notifications={notifications}
               onClearNotifications={clearAllNotifications}
+              onOpenSettings={(section) => { setSettingsInitialSection(section); setSettingsModalOpen(true); }}
             />
           )}
         </div>