feat: implement WebSocket real-time progress updates

- Add ProgressService for centralized progress tracking and broadcasting
- Integrate ProgressService with DownloadService for download progress
- Integrate ProgressService with AnimeService for scan progress
- Add progress-related WebSocket message models (ScanProgress, ErrorNotification, etc.)
- Initialize ProgressService with WebSocket callback in application startup
- Add comprehensive unit tests for ProgressService
- Update infrastructure.md with ProgressService documentation
- Remove completed WebSocket Real-time Updates task from instructions.md

The ProgressService provides:
- Real-time progress tracking for downloads, scans, and queue operations
- Automatic progress percentage calculation
- Progress lifecycle management (start, update, complete, fail, cancel)
- WebSocket integration for instant client updates
- Progress history with size limits
- Thread-safe operations using asyncio locks
- Support for metadata and custom messages

Benefits:
- Decoupled progress tracking from WebSocket broadcasting
- Single reusable service across all components
- Supports multiple concurrent operations efficiently
- Centralized progress tracking simplifies monitoring
- Instant feedback to users on long-running operations

src/server/fastapi_app.py

@@ -29,6 +29,8 @@ from src.server.controllers.error_controller import (
 from src.server.controllers.health_controller import router as health_router
 from src.server.controllers.page_controller import router as page_router
 from src.server.middleware.auth import AuthMiddleware
+from src.server.services.progress_service import get_progress_service
+from src.server.services.websocket_service import get_websocket_service
 
 # Initialize FastAPI app
 app = FastAPI(
@@ -74,6 +76,23 @@ async def startup_event():
         # Initialize SeriesApp with configured directory
         if settings.anime_directory:
             series_app = SeriesApp(settings.anime_directory)
+        
+        # Initialize progress service with websocket callback
+        progress_service = get_progress_service()
+        ws_service = get_websocket_service()
+        
+        async def broadcast_callback(
+            message_type: str, data: dict, room: str
+        ):
+            """Broadcast progress updates via WebSocket."""
+            message = {
+                "type": message_type,
+                "data": data,
+            }
+            await ws_service.manager.broadcast_to_room(message, room)
+        
+        progress_service.set_broadcast_callback(broadcast_callback)
+        
         print("FastAPI application started successfully")
     except Exception as e:
         print(f"Error during startup: {e}")