feat(J): WebSocket live-events + replace polling + fix ffmpeg turntable timeout

- fix(render): ffmpeg overlay=0:0 -> overlay=0:0:shortest=1 to prevent hang on finite PNG sequences
- feat(ws): add core/websocket.py ConnectionManager + Redis Pub/Sub subscriber loop
- feat(ws): add /api/ws WebSocket endpoint with JWT query-param auth in main.py
- feat(ws): emit render_complete/failed + cad_processing_complete events from step_tasks.py
- feat(ws): emit order_status_change events from orders router
- feat(ws): add beat_tasks.py broadcast_queue_status task (every 10s via Redis __broadcast__)
- feat(frontend): add useWebSocket hook with auto-reconnect (exponential backoff, 25s ping)
- feat(frontend): add WebSocketContext + WebSocketProvider wrapping App
- refactor(frontend): remove polling from WorkerActivity (was 5s/3s) + OrderDetail (was 5s)
- refactor(frontend): reduce polling in Layout (8s->60s) + NotificationCenter (15s->60s)
- docs: add ffmpeg shortest=1 + WebSocket JWT auth learnings to LEARNINGS.md

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/api/routers/orders.py

@@ -486,6 +486,20 @@ async def submit_order(
     from app.services.pricing_service import refresh_order_price
     await refresh_order_price(db, order.id)
     await db.refresh(order)
+
+    # Broadcast WebSocket event for live UI updates
+    try:
+        from app.core.websocket import manager as _ws_mgr
+        _tid = str(user.tenant_id) if user.tenant_id else None
+        if _tid:
+            await _ws_mgr.broadcast_to_tenant(_tid, {
+                "type": "order_status_change",
+                "order_id": str(order.id),
+                "status": "submitted",
+            })
+    except Exception:
+        pass
+
     return order