fix async handling in SerieScanner and add image_downloader cleanup

- SerieScanner.scan() now detects running event loop and uses create_task()
  when already in async context, avoids RuntimeError
- NFOService.close() now also closes image_downloader to prevent resource leaks
- Add integration tests for TMDBClient lifecycle management

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

tests/unit/test_tmdb_client.py

@@ -444,6 +444,77 @@ class TestTMDBClientSessionLeak:
             "Unexpected warning about unclosed session"
 
 
+class TestTMDBClientLifecycleIntegration:
+    """Integration tests for TMDBClient lifecycle management."""
+    
+    @pytest.mark.asyncio
+    async def test_context_manager_no_resource_warning(self, caplog):
+        """Test async with TMDBClient produces no ResourceWarning."""
+        import logging
+        import warnings
+        caplog.set_level(logging.WARNING)
+        
+        # Use context manager properly - should not leak
+        async with TMDBClient(api_key="test_key") as client:
+            await client._ensure_session()
+            assert client.session is not None
+        
+        # Session should be closed after context exit
+        assert client.session is None or client.session.closed
+    
+    @pytest.mark.asyncio
+    async def test_exception_safety_during_api_call(self, caplog):
+        """Test session is closed even when exception raised during API call."""
+        import logging
+        caplog.set_level(logging.WARNING)
+        
+        close_called = False
+        
+        class TrackingSession:
+            def __init__(self):
+                self.closed = False
+            
+            async def close(self):
+                nonlocal close_called
+                close_called = True
+                self.closed = True
+            
+            async def get(self, url, **kwargs):
+                raise TMDBAPIError("Simulated API failure")
+        
+        client = TMDBClient(api_key="test_key")
+        client.session = TrackingSession()
+        
+        # Exception during context should still close session
+        with pytest.raises(TMDBAPIError):
+            async with client:
+                raise TMDBAPIError("Simulated API failure")
+        
+        assert close_called, "Session was not closed after API exception"
+    
+    @pytest.mark.asyncio
+    async def test_reuse_session_across_multiple_requests(self, caplog):
+        """Test session is reused across multiple requests without leaks."""
+        import logging
+        caplog.set_level(logging.WARNING)
+        
+        client = TMDBClient(api_key="test_key")
+        
+        async with client as c:
+            # First request
+            await c._ensure_session()
+            session1 = c.session
+            
+            # Second request should reuse same session
+            await c._ensure_session()
+            session2 = c.session
+            
+            assert session1 is session2, "Session should be reused"
+        
+        # After context exit, session should be closed
+        assert client.session is None or client.session.closed
+
+
 class TestTMDBClientConnectorClosed:
     """Test handling of 'Connector is closed' errors."""