fix: auto-fix code issues (cron)

- 修复重复导入/字段
- 修复异常处理
- 修复PEP8格式问题
- 添加类型注解

backend/growth_manager.py

@@ -369,7 +369,7 @@ class GrowthManager:
         self.segment_write_key = os.getenv("SEGMENT_WRITE_KEY", "")
         self.sendgrid_api_key = os.getenv("SENDGRID_API_KEY", "")
 
-    def _get_db(self):
+    def _get_db(self) -> None:
         """获取数据库连接"""
         conn = sqlite3.connect(self.db_path)
         conn.row_factory = sqlite3.Row