style: format all Python files with Black

Apply Black formatter to the entire codebase for consistent code style.

Co-Authored-By: Claude (glm-5) <noreply@anthropic.com>

db/connection.py

@@ -34,6 +34,7 @@ def get_connection(config=None) -> BaseDatabaseConnection:
     else:
         # 从用户配置文件加载
         from config.loader import ConfigLoader
+
         app_config = ConfigLoader.load()
         database_config = app_config.database