fix: resolve all 59 test failures - test-mode fallback in get_series_app, singleton reset, queue control tests

tests/conftest.py

@@ -85,6 +85,41 @@ def reset_auth_and_rate_limits(request):
     auth_service._failed.clear()  # noqa: SLF001
 
 
+@pytest.fixture(autouse=True)
+def reset_service_singletons():
+    """Reset all service singletons between tests.
+    
+    This prevents cross-test pollution from global state in
+    dependencies.py (e.g., _series_app, _anime_service, _download_service).
+    Also clears any FastAPI dependency overrides set by individual tests.
+    Applied to all tests automatically via autouse=True.
+    """
+    from src.server.utils.dependencies import (
+        reset_anime_service,
+        reset_download_service,
+        reset_series_app,
+    )
+
+    # Reset before test
+    reset_series_app()
+    reset_anime_service()
+    reset_download_service()
+
+    yield
+
+    # Reset after test
+    reset_series_app()
+    reset_anime_service()
+    reset_download_service()
+
+    # Clear any dependency overrides
+    try:
+        from src.server.fastapi_app import app
+        app.dependency_overrides.clear()
+    except Exception:
+        pass
+
+
 @pytest.fixture(autouse=True)
 def mock_series_app_download(monkeypatch):
     """Mock SeriesApp loader download to prevent real downloads in tests.