Migrate download queue from JSON to SQLite database

- Created QueueRepository adapter in src/server/services/queue_repository.py
- Refactored DownloadService to use repository pattern instead of JSON
- Updated application startup to initialize download service from database
- Updated all test fixtures to use MockQueueRepository
- All 1104 tests passing

tests/integration/test_download_progress_integration.py

@@ -72,11 +72,14 @@ async def anime_service(mock_series_app, progress_service):
 
 @pytest.fixture
 async def download_service(anime_service, progress_service):
-    """Create a DownloadService."""
+    """Create a DownloadService with mock queue repository."""
+    from tests.unit.test_download_service import MockQueueRepository
+    
+    mock_repo = MockQueueRepository()
     service = DownloadService(
         anime_service=anime_service,
         progress_service=progress_service,
-        persistence_path="/tmp/test_integration_progress_queue.json",
+        queue_repository=mock_repo,
     )
     yield service
     await service.stop()