feat: global Docker health indicator and graceful degradation

- GET /api/health endpoint returning Docker connectivity status
- Sidebar shows Docker connection dot (green=connected, red=disconnected)
- Stale scanner returns store-only results when Docker is unavailable
- Polls health every 30s

web/src/lib/sse.ts

@@ -5,6 +5,8 @@
  * event streams (deploy logs and instance status changes).
  */
 
+import { getAuthToken } from './auth';
+
 // ── Types ──────────────────────────────────────────────────────────
 
 export type SSEEventType = 'deploy_log' | 'instance_status' | 'deploy_status' | 'event_log';
@@ -97,7 +99,7 @@ export function connectSSE(url: string, options: SSEOptions): SSEConnection {
 		if (closed) return;
 
 		// Append auth token as query param (EventSource doesn't support custom headers).
-		const token = typeof localStorage !== 'undefined' ? localStorage.getItem('auth_token') : null;
+		const token = getAuthToken();
 		const authUrl = token ? `${url}${url.includes('?') ? '&' : '?'}token=${encodeURIComponent(token)}` : url;
 		eventSource = new EventSource(authUrl);