feat(init): 添加完整的认证和业务路由模块

- 实现微信登录、手机号绑定、token验证和登出功能
- 添加打卡系统，支持正常、迟到、请假等状态记录
- 集成课程投票功能，支持多课程选择和评分评论
- 开发反馈系统，支持图文反馈提交和管理员处理
- 构建首页页面模块，动态展示学习资源和个人信息
- 设计计划管理系统，支持周/月/年计划制定和跟踪
- 实现小组计划统计和历史记录查询功能
- 完善用户认证会话管理和数据库交互逻辑

db.py

@@ -0,0 +1,97 @@
+"""Database access with a PyMySQL connection pool.
+
+Each fetch/execute borrows a pooled connection and returns it on close().
+Pool settings are read from environment (DB_POOL_*), so nothing here depends
+on config.py and the pool can be shared safely across threads via DBUtils.
+"""
+import os
+import logging
+import threading
+
+import pymysql
+from dbutils.pooled_db import PooledDB
+
+from . import config
+
+
+logger = logging.getLogger(__name__)
+
+
+def _pool_args(database):
+    return dict(
+        mincached=int(os.environ.get("DB_POOL_MIN_CACHED", "1")),
+        maxcached=int(os.environ.get("DB_POOL_MAX_CACHED", "5")),
+        maxconnections=int(os.environ.get("DB_POOL_MAX_CONNECTIONS", "10")),
+        blocking=True,
+        maxusage=int(os.environ.get("DB_POOL_MAX_USAGE", "100")),
+        ping=1,
+        host=config.MYSQL_HOST,
+        port=config.MYSQL_PORT,
+        user=config.MYSQL_USER,
+        password=config.MYSQL_PASSWORD,
+        database=database,
+        charset="utf8mb4",
+        connect_timeout=5,
+        read_timeout=5,
+    )
+
+
+_pools = {}
+_pools_lock = threading.Lock()
+
+
+def _get_pool(database):
+    key = database or config.MYSQL_DB
+    with _pools_lock:
+        pool = _pools.get(key)
+        if pool is None:
+            pool = PooledDB(creator=pymysql, **_pool_args(key))
+            _pools[key] = pool
+        return pool
+
+
+def _connect(db=None):
+    """Borrow a pooled connection (close() returns it to the pool)."""
+    return _get_pool(db).connection()
+
+
+def fetch_one(sql, args=None, db=None):
+    conn = _connect(db)
+    try:
+        with conn.cursor(pymysql.cursors.DictCursor) as cur:
+            cur.execute(sql, args or ())
+            return cur.fetchone()
+    finally:
+        conn.close()
+
+
+def fetch_all(sql, args=None, db=None):
+    conn = _connect(db)
+    try:
+        with conn.cursor(pymysql.cursors.DictCursor) as cur:
+            cur.execute(sql, args or ())
+            return cur.fetchall()
+    finally:
+        conn.close()
+
+
+def execute(sql, args=None, db=None):
+    conn = _connect(db)
+    try:
+        with conn.cursor() as cur:
+            cur.execute(sql, args or ())
+            lastrowid = cur.lastrowid
+        conn.commit()
+        return lastrowid
+    finally:
+        conn.close()
+
+
+def close_all():
+    """Close every pooled connection (used by tests / reload hooks)."""
+    with _pools_lock:
+        for key in list(_pools):
+            try:
+                _pools.pop(key).close()
+            except Exception:
+                logger.exception("关闭数据库连接池失败: %s", key)