feat: Complete watchlist & auto-download system with UI

## Backend Implementation (100% Complete)

### Core Components
- **WatchlistManager**: JSON-based storage with full CRUD operations
  - User-scoped data access for multi-tenant support
  - Statistics and query functions
  - Settings management with persistence

- **EpisodeChecker**: Automatic new episode detection
  - Checks for new episodes using existing downloaders
  - Automatic download with error handling
  - Manual and scheduled check support
  - Lazy initialization to avoid circular imports

- **AutoDownloadScheduler**: APScheduler-based periodic checking
  - Configurable intervals (1-168 hours)
  - Start/stop/restart controls
  - Next run time tracking

### API Endpoints (15 endpoints)
- POST /api/watchlist - Add anime to watchlist
- GET /api/watchlist - Get user's watchlist (with status filter)
- GET /api/watchlist/{id} - Get specific item
- PUT /api/watchlist/{id} - Update item
- DELETE /api/watchlist/{id} - Delete item
- POST /api/watchlist/{id}/check - Check for new episodes
- POST /api/watchlist/{id}/pause - Pause tracking
- POST /api/watchlist/{id}/resume - Resume tracking
- GET /api/watchlist/settings - Get settings
- PUT /api/watchlist/settings - Update settings
- GET /api/watchlist/stats - Get statistics
- POST /api/watchlist/check-all - Check all items
- GET /api/watchlist/scheduler/status - Scheduler status
- POST /api/watchlist/scheduler/start - Start scheduler
- POST /api/watchlist/scheduler/stop - Stop scheduler

### Bug Fixes
- Fixed WatchlistManager.update() to accept both dict and WatchlistItemUpdate
- Added asyncio import to AutoDownloadScheduler for event loop detection
- Improved scheduler start() with better error handling

## Frontend Implementation (100% Complete)

### UI Components
- **Watchlist Page** (/watchlist)
  - Scheduler status panel with start/stop/check all buttons
  - Filter tabs (all/active/paused/completed)
  - Statistics display with color-coded cards
  - Watchlist items with pause/resume/delete controls
  - Auto-refresh every 30 seconds
  - Authentication check

- **Settings Modal**
  - Check interval configuration (1-168h)
  - Auto-download toggle
  - Max concurrent downloads slider
  - Notifications toggle
  - Live settings update with scheduler restart

- **"Suivre" Button**
  - Added to anime search result cards
  - Purple gradient with heart icon
  - Quick-add to watchlist functionality
  - State tracking (disabled when already in watchlist)

### JavaScript Files
- **static/js/watchlist.js**: API client functions
  - All watchlist API calls with token auth
  - Error handling and response parsing

- **static/js/watchlist-ui.js**: UI functions
  - Display watchlist with stats
  - Handle add/pause/resume/delete
  - Filter by status
  - Settings modal management

- **static/js/tabs.js**: Watchlist tab handler
  - Redirects to /watchlist page

## Testing

### Test Suite (test_watchlist_simple.py)
All tests passing (3/3):

1. **Watchlist Manager Tests** ✅
   - Create/read/update/delete operations
   - User-scoped queries
   - Statistics generation
   - Check time updates

2. **Settings Tests** ✅
   - Get current settings
   - Update settings with validation
   - Reset to defaults

3. **Scheduler Tests** ✅
   - Start/stop/restart controls
   - Running status verification
   - Next run time tracking

### Dependencies
- APScheduler 3.11.0 installed in virtual environment
- tzlocal 5.3.1 (APScheduler dependency)

## Documentation
- docs/WATCHLIST_AUTO_DOWNLOAD.md: Complete system documentation
  - API endpoints with examples
  - Architecture overview
  - Usage examples
  - Troubleshooting guide

Generated with [Claude Code](https://claude.ai/code)
via [Happy](https://happy.engineering)

Co-Authored-By: Claude <noreply@anthropic.com>
Co-Authored-By: Happy <yesreply@happy.engineering>

app/watchlist.py

@@ -155,14 +155,24 @@ class WatchlistManager:
         logger.info(f"Added anime to watchlist: {watchlist_item.anime_title} (ID: {item_id})")
         return watchlist_item
 
-    def update(self, item_id: str, update_data: WatchlistItemUpdate) -> Optional[WatchlistItem]:
-        """Update a watchlist item"""
+    def update(self, item_id: str, update_data) -> Optional[WatchlistItem]:
+        """Update a watchlist item
+
+        Args:
+            item_id: Item ID to update
+            update_data: WatchlistItemUpdate object or dict with fields to update
+        """
         item = self.watchlist.get(item_id)
         if not item:
             return None
 
+        # Handle both dict and WatchlistItemUpdate
+        if isinstance(update_data, dict):
+            update_dict = update_data
+        else:
+            update_dict = update_data.model_dump(exclude_unset=True)
+
         # Update fields
-        update_dict = update_data.model_dump(exclude_unset=True)
         for field, value in update_dict.items():
             if value is not None:
                 setattr(item, field, value)