fix: Improve Docker container shutdown handling

- Add proper signal handlers for graceful shutdown of all components
- Implement WebhookBatcher.shutdown() to properly close ThreadPoolExecutor and cancel timers
- Add NFOGuardDatabase.close() method to close thread-local database connections
- Increase uvicorn graceful shutdown timeout to 15 seconds
- Add cleanup in finally block to ensure resources are freed even if signal handler fails
- Reduce logging and server header overhead for better performance

This should resolve Docker container shutdown issues where containers don't respond to SIGTERM properly.

Bump version to 2.1.1

🤖 Generated with [Claude Code](https://claude.ai/code)

core/database.py

@@ -271,4 +271,13 @@ class NFOGuardDatabase:
                 "movies_with_video": movies_with_video,
                 "processing_history_count": history_count,
                 "database_size_mb": round(self.db_path.stat().st_size / 1024 / 1024, 2)
-            }
+            }
+    
+    def close(self):
+        """Close all database connections"""
+        if hasattr(self._local, 'connection'):
+            try:
+                self._local.connection.close()
+                delattr(self._local, 'connection')
+            except Exception:
+                pass  # Connection may already be closed