Add real-time WebSocket task progress with multi-job drawer

Replace 5s HTTP polling with WebSocket-based real-time updates for task
progress. Celery workers publish progress to Redis pub/sub channels;
a FastAPI WebSocket endpoint subscribes and forwards to the browser.
Polling is kept as a 30s fallback when WebSocket is unavailable.

The task progress drawer now supports multiple concurrent jobs with a
tab bar for switching between scrape and POI distance tasks.

Backend:
- Add services/task_progress_publisher.py (Redis pub/sub bridge)
- Add api/ws_routes.py (WebSocket endpoint with JWT auth)
- Publish progress from listing_tasks and poi_tasks
- Publish REVOKED via pub/sub on cancel/clear to fix stuck UI

Frontend:
- Add useTaskWebSocket hook with reconnection and keepalive
- Add TaskState and WS message types
- TaskIndicator: WS-driven updates with polling fallback
- TaskProgressDrawer: multi-job tabs, POI phase timeline
- Guard against WS overwriting local cancel state

frontend/src/constants/index.ts

@@ -59,5 +59,8 @@ export const DEFAULT_FORM_VALUES = {
 
 // Polling intervals
 export const POLLING_INTERVALS = {
-  TASK_STATUS_MS: 5000, // 5 seconds
+  TASK_STATUS_MS: 30000, // 30 seconds (fallback when WebSocket is unavailable)
 } as const;
+
+// WebSocket paths
+export const WS_TASKS_PATH = '/api/ws/tasks';