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/base.py

@@ -0,0 +1,52 @@
+"""通用 HTTP 爬虫基类 - 为基于 HTTP 请求的插件提供封装"""
+import random
+import asyncio
+import aiohttp
+from typing import List
+from app.core.plugin_system import BaseCrawlerPlugin
+
+
+class BaseHTTPPlugin(BaseCrawlerPlugin):
+    """基于 HTTP 的爬虫插件基类"""
+
+    def __init__(self):
+        super().__init__()
+        self.user_agents = [
+            "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36",
+            "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/119.0.0.0 Safari/537.36",
+            "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/118.0.0.0 Safari/537.36",
+            "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:109.0) Gecko/20100101 Firefox/121.0",
+        ]
+        self.urls: List[str] = []
+        self.current_url: str = ""
+
+    def get_headers(self) -> dict:
+        return {
+            "User-Agent": random.choice(self.user_agents),
+            "Accept": "text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8",
+            "Accept-Language": "zh-CN,zh;q=0.8,zh-TW;q=0.7,zh-HK;q=0.5,en-US;q=0.3,en;q=0.2",
+            "Connection": "keep-alive",
+        }
+
+    async def fetch(self, url: str, timeout: float = 10.0, retries: int = 3) -> str:
+        """异步抓取指定 URL 的 HTML 内容"""
+        headers = self.get_headers()
+        async with aiohttp.ClientSession(headers=headers) as session:
+            for attempt in range(retries):
+                try:
+                    async with session.get(
+                        url, timeout=aiohttp.ClientTimeout(total=timeout)
+                    ) as response:
+                        if response.status == 200:
+                            content = await response.read()
+                            encoding = response.get_encoding()
+                            if encoding == "utf-8" or not encoding:
+                                try:
+                                    return content.decode("utf-8")
+                                except UnicodeDecodeError:
+                                    return content.decode("gbk", errors="ignore")
+                            return content.decode(encoding, errors="ignore")
+                except Exception:
+                    pass
+                await asyncio.sleep(random.uniform(1, 3))
+        return ""