Add Video Learning Agent for short video platforms

Features:
- VideoLearningAgent for automated video watching on Douyin/Kuaishou/TikTok
- Web dashboard UI for video learning sessions
- Real-time progress tracking with screenshot capture
- App detection using get_current_app() for accurate recording
- Session management with pause/resume/stop controls

Technical improvements:
- Simplified video detection logic using direct app detection
- Full base64 hash for sensitive screenshot change detection
- Immediate stop when target video count is reached
- Fixed circular import issues with ModelConfig

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

dashboard/api/__init__.py

@@ -5,9 +5,11 @@ API endpoints for the dashboard.
 from dashboard.api.devices import router as devices_router
 from dashboard.api.tasks import router as tasks_router
 from dashboard.api.websocket import router as websocket_router
+from dashboard.api.video_learning import router as video_learning_router
 
 __all__ = [
     "devices_router",
     "tasks_router",
     "websocket_router",
+    "video_learning_router",
 ]