修复37项安全漏洞和Bug

高危修复:
- app.py: 添加ip_rate_limit_lock线程锁保护IP限流字典
- app.py: 添加validate_ip_port()验证代理IP/端口范围
- database.py: SQL字段名白名单验证防止注入
- playwright_automation.py: 改进浏览器进程强制清理逻辑

中危修复:
- database.py: 统一时区处理函数get_cst_now()
- database.py: 消除循环导入,移动app_security导入到顶部
- playwright_automation.py: 所有bare except改为except Exception
- app_config.py: dotenv导入失败警告+安全配置检查
- db_pool.py: 添加详细异常堆栈日志
- app_security.py: 用户名过滤零宽字符
- database.py: delete_old_task_logs分批删除避免锁表

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

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

db_pool.py

@@ -101,7 +101,10 @@ class ConnectionPool:
             except Exception as close_error:
                 print(f"关闭多余连接失败: {close_error}")
         except Exception as e:
+            # Bug fix: 记录详细的异常堆栈，便于调试
+            import traceback
             print(f"归还连接失败(未知错误): {e}")
+            print(f"异常堆栈:\n{traceback.format_exc()}")
             try:
                 conn.close()
             except Exception as close_error: