feature: 数据库连接与SQL集中管理，提高代码可读性

db/sign_in.py

@@ -0,0 +1,64 @@
+# -*- coding: utf-8 -*-
+from datetime import datetime
+from typing import Dict, Optional
+
+from db.base import BaseDBOperator
+from db.connection import DBConnectionManager
+
+
+class SignInDB(BaseDBOperator):
+    """签到系统相关数据库操作"""
+    
+    def __init__(self, db_manager: DBConnectionManager):
+        super().__init__(db_manager)
+        
+    def initialize_table(self) -> bool:
+        """初始化签到表"""
+        sql = """
+        CREATE TABLE IF NOT EXISTS t_sign_record (
+            id BIGINT AUTO_INCREMENT PRIMARY KEY,
+            wx_id VARCHAR(100) NOT NULL,
+            group_id VARCHAR(100) NOT NULL,
+            wx_nick_name VARCHAR(100) NOT NULL,
+            points INT DEFAULT 0,
+            sign_stat DATETIME,
+            signin_streak INT DEFAULT 0,
+            create_time DATETIME DEFAULT CURRENT_TIMESTAMP,
+            update_time DATETIME DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
+            UNIQUE KEY unique_sign (wx_id, group_id)
+        )
+        """
+        return self.execute_update(sql)
+    
+    def get_user_record(self, wx_id: str, group_id: str) -> Optional[Dict]:
+        """获取用户签到记录"""
+        sql = """
+        SELECT wx_id, group_id, wx_nick_name, points, sign_stat, signin_streak
+        FROM t_sign_record 
+        WHERE wx_id = %s AND group_id = %s
+        """
+        return self.execute_query(sql, (wx_id, group_id), fetch_one=True)
+    
+    def update_sign_record(self, wx_id: str, group_id: str, wx_nick_name: str, 
+                          points_to_add: int, sign_time: datetime, streak: int) -> bool:
+        """更新签到记录"""
+        sql = """
+        UPDATE t_sign_record 
+        SET wx_nick_name = %s, points = points + %s, 
+            sign_stat = %s, signin_streak = %s,
+            update_time = %s
+        WHERE wx_id = %s AND group_id = %s
+        """
+        params = (wx_nick_name, points_to_add, sign_time, streak, sign_time, wx_id, group_id)
+        return self.execute_update(sql, params)
+    
+    def create_sign_record(self, wx_id: str, group_id: str, wx_nick_name: str, 
+                          points: int, sign_time: datetime, streak: int) -> bool:
+        """创建签到记录"""
+        sql = """
+        INSERT INTO t_sign_record 
+        (wx_id, group_id, wx_nick_name, points, sign_stat, signin_streak)
+        VALUES (%s, %s, %s, %s, %s, %s)
+        """
+        params = (wx_id, group_id, wx_nick_name, points, sign_time, streak)
+        return self.execute_update(sql, params)