feat: task 2.9 connection status + per-device staleness fade — Phase 2 done

- src/live/last-seen.ts: formatLastSeen(ts, now) — "now" / "Ns ago" /
  "Nm ago" / "HH:MM".
- src/live/use-staleness.ts: useStalenessTick(intervalMs=1000) hook
  re-renders subscribers every interval with the current epoch ms.
- src/ui/components/connection-chip.tsx: <ConnectionChip /> bottom-left,
  three states (connected / connecting+reconnecting / disconnected),
  aria-live polite + role status.
- src/map/layers/map-positions.tsx: every FeatureProps now carries
  staleSec; both symbol layers interpolate icon-opacity (and text-opacity
  on the non-selected layer) on staleSec — 0-60s full opacity,
  5min faded, 30min very faded. Update effect rebuilds features at the
  staleness tick rate (1Hz).
- src/routes/_authed/monitor.tsx: renders <ConnectionChip />.
- src/live/index.ts: re-exports formatLastSeen + useStalenessTick.

Strategy A (faded marker via interpolation) chosen over Strategy B
(separate warning-badge layer) per the task's open-question
resolution; simpler and easier to extend later.

Deviations:
1. stalenessTick is its own hook in src/live/use-staleness.ts rather
   than a property on the position store — keeps the store clean of
   UI-driven re-render concerns; the hook is reusable.
2. <DeviceLastSeen deviceId> standalone component skipped — the SPA
   doesn't have a sidebar yet (Phase 3.4); the per-marker fade IS the
   indicator for v1.

Bundle: main 396KB / 121KB gz — small bump from 2.8.

🎉 Phase 2 — Live monitoring map — complete. All 9 tasks shipped.
End-to-end: login -> /monitor -> event auto-selects -> snapshot
positions render -> live updates flow via WS through the rAF
coalescer -> staleness fades stale markers -> connection chip
surfaces WS state. Dogfood-blocking work for Rally Albania 2026 done.

src/routes/_authed/monitor.tsx

@@ -14,6 +14,7 @@ import { MapView } from '@/map/core/map-view';
 import { TrailsToggle } from '@/map/core/trails-toggle';
 import { MapPositions } from '@/map/layers/map-positions';
 import { MapTrails } from '@/map/layers/map-trails';
+import { ConnectionChip } from '@/ui/components/connection-chip';
 import { EventPicker } from '@/ui/components/event-picker';
 
 export const Route = createFileRoute('/_authed/monitor')({
@@ -75,6 +76,11 @@ function MonitorPage() {
         */}
         <MapDefaultCamera />
         <MapSelectedDevice />
+        {/*
+          Status indicator. Bottom-left, subtle when connected, louder
+          when reconnecting / offline.
+        */}
+        <ConnectionChip />
       </MapView>
     </div>
   );