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/FleetView.tsx

@@ -27,6 +27,7 @@ import { apiFetch, fetchForNode } from '@/lib/api';
 import { useLicense } from '@/context/LicenseContext';
 import { PaidGate } from './PaidGate';
 import FleetSnapshots from './FleetSnapshots';
+import { FleetConfiguration } from './fleet/FleetConfiguration';
 import { toast } from '@/components/ui/toast-store';
 import { LabelDot } from './LabelPill';
 import { type Label as StackLabel, type LabelColor } from './label-types';
@@ -1041,6 +1042,11 @@ export function FleetView({ onNavigateToNode }: FleetViewProps) {
                                     </TabsTrigger>
                                 </TabsHighlightItem>
                             )}
+                            <TabsHighlightItem value="configuration">
+                                <TabsTrigger value="configuration">
+                                    <SlidersHorizontal className="w-4 h-4 mr-1.5" />Status
+                                </TabsTrigger>
+                            </TabsHighlightItem>
                         </TabsHighlight>
                     </TabsList>
                     <div className="flex items-center gap-2">
@@ -1337,6 +1343,9 @@ export function FleetView({ onNavigateToNode }: FleetViewProps) {
                         <FleetSnapshots />
                     </TabsContent>
                 )}
+                <TabsContent value="configuration">
+                    <FleetConfiguration />
+                </TabsContent>
             </Tabs>
 
             {/* Reconnecting overlay shown when local node is updating */}