feat: SMTP配额自动重置（北京时间凌晨0点）

- 添加reset_smtp_daily_quota函数主动重置配额
- 添加定时任务在北京时间00:00自动重置SMTP配额
- 保留被动重置作为备份机制

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

email_service.py

@@ -933,6 +933,23 @@ def _update_email_stats(email_type: str, success: bool):
         conn.commit()
 
 
+def reset_smtp_daily_quota():
+    """重置所有SMTP配置的每日发送计数（北京时间凌晨0点调用）"""
+    today = get_beijing_today()
+    with db_pool.get_db() as conn:
+        cursor = conn.cursor()
+        cursor.execute("""
+            UPDATE smtp_configs
+            SET daily_sent = 0, daily_reset_date = ?
+            WHERE daily_reset_date != ? OR daily_reset_date IS NULL OR daily_reset_date = ''
+        """, (today, today))
+        updated = cursor.rowcount
+        conn.commit()
+        if updated > 0:
+            print(f"[邮件服务] 已重置 {updated} 个SMTP配置的每日配额")
+        return updated
+
+
 def get_email_stats() -> Dict[str, Any]:
     """获取邮件统计"""
     with db_pool.get_db() as conn: