重构: 迁移后端代码到 app 目录，前端移动到 WebUI，添加完整测试套件

主要变更:
- 后端代码从根目录迁移到 app/ 目录
- 前端代码从 frontend/ 重命名为 WebUI/
- 更新所有导入路径以适配新结构
- 提取公共 API 响应函数到 app/api/common.py
- 精简验证器服务代码
- 更新启动脚本和文档

测试:
- 新增完整测试套件 (tests/)
- 单元测试: 模型、仓库层
- 集成测试: 覆盖所有 22+ API 端点
- E2E 测试: 4个完整工作流场景
- 添加 pytest 配置和测试运行脚本

app/plugins/yundaili.py

@@ -0,0 +1,51 @@
+import re
+from typing import List
+from bs4 import BeautifulSoup
+from app.core.plugin_system import ProxyRaw
+from app.plugins.base import BaseHTTPPlugin
+from app.core.log import logger
+
+VALID_PROTOCOLS = ("http", "https", "socks4", "socks5")
+
+
+class YunDaiLiPlugin(BaseHTTPPlugin):
+    name = "yundaili"
+    display_name = "云代理"
+    description = "从云代理网站爬取免费代理"
+
+    def __init__(self):
+        super().__init__()
+        self.urls = [
+            f"http://www.ip3366.net/free/?stype=1&page={i}" for i in range(1, 6)
+        ] + [
+            f"http://www.ip3366.net/free/?stype=2&page={i}" for i in range(1, 6)
+        ]
+
+    async def crawl(self) -> List[ProxyRaw]:
+        results = []
+        for url in self.urls:
+            html = await self.fetch(url, timeout=15)
+            if not html:
+                continue
+            soup = BeautifulSoup(html, "lxml")
+            list_table = soup.find("div", id="list")
+            if not list_table:
+                continue
+            table = list_table.find("table")
+            if not table:
+                continue
+
+            for row in table.find_all("tr"):
+                tds = row.find_all("td")
+                if len(tds) >= 5:
+                    ip = tds[0].get_text(strip=True)
+                    port = tds[1].get_text(strip=True)
+                    protocol = tds[4].get_text(strip=True).lower() if len(tds) > 4 else "http"
+                    if protocol not in VALID_PROTOCOLS:
+                        protocol = "http"
+                    if re.match(r"^\d+\.\d+\.\d+\.\d+$", ip) and port.isdigit():
+                        results.append(ProxyRaw(ip, int(port), protocol))
+
+        if results:
+            logger.info(f"{self.display_name} 解析完成，获得 {len(results)} 个潜在代理")
+        return results