feat(monitor): implement code review fixes and real-time WebSocket monitoring

Backend Improvements (11 fixes applied):

Critical Fixes:
- Add lock protection for browser pool access in monitor stats
- Ensure async track_janitor_event across all call sites
- Improve error handling in monitor request tracking (already in place)

Important Fixes:
- Replace fire-and-forget Redis with background persistence worker
- Add time-based expiry for completed requests/errors (5min cleanup)
- Implement input validation for monitor route parameters
- Add 4s timeout to timeline updater to prevent hangs
- Add warning when killing browsers with active requests
- Implement monitor cleanup on shutdown with final persistence
- Document memory estimates with TODO for actual tracking

Frontend Enhancements:

WebSocket Real-time Updates:
- Add WebSocket endpoint at /monitor/ws for live monitoring
- Implement auto-reconnect with exponential backoff (max 5 attempts)
- Add graceful fallback to HTTP polling on WebSocket failure
- Send comprehensive updates every 2 seconds (health, requests, browsers, timeline, events)

UI/UX Improvements:
- Add live connection status indicator with pulsing animation
  - Green "Live" = WebSocket connected
  - Yellow "Connecting..." = Attempting connection
  - Blue "Polling" = Fallback to HTTP polling
  - Red "Disconnected" = Connection failed
- Restore original beautiful styling for all sections
- Improve request table layout with flex-grow for URL column
- Add browser type text labels alongside emojis
- Add flex layout to browser section header

Testing:
- Add test-websocket.py for WebSocket validation
- All 7 integration tests passing successfully

Summary: 563 additions across 6 files

deploy/docker/server.py

@@ -119,6 +119,7 @@ async def lifespan(_: FastAPI):
     # Initialize monitor
     monitor_module.monitor_stats = MonitorStats(redis)
     await monitor_module.monitor_stats.load_from_redis()
+    monitor_module.monitor_stats.start_persistence_worker()
 
     # Initialize browser pool
     await init_permanent(BrowserConfig(
@@ -135,6 +136,14 @@ async def lifespan(_: FastAPI):
     # Cleanup
     app.state.janitor.cancel()
     app.state.timeline_updater.cancel()
+
+    # Monitor cleanup (persist stats and stop workers)
+    from monitor import get_monitor
+    try:
+        await get_monitor().cleanup()
+    except Exception as e:
+        logger.error(f"Monitor cleanup failed: {e}")
+
     await close_all()
 
 async def _timeline_updater():
@@ -143,7 +152,9 @@ async def _timeline_updater():
     while True:
         await asyncio.sleep(5)
         try:
-            await get_monitor().update_timeline()
+            await asyncio.wait_for(get_monitor().update_timeline(), timeout=4.0)
+        except asyncio.TimeoutError:
+            logger.warning("Timeline update timeout after 4s")
         except Exception as e:
             logger.warning(f"Timeline update error: {e}")