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

tests/e2e/__init__.py

@@ -0,0 +1 @@
+"""端到端测试"""

tests/e2e/test_full_workflow.py

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+"""完整工作流 E2E 测试
+
+这些测试模拟真实用户场景，验证整个系统的集成功能。
+"""
+import pytest
+
+
+class TestFullWorkflow:
+    """测试完整工作流"""
+
+    @pytest.mark.asyncio
+    async def test_proxy_management_workflow(self, client):
+        """测试代理管理完整工作流
+        
+        场景：
+        1. 查看统计信息
+        2. 列出代理
+        3. 触发爬取
+        4. 查看更新后的统计
+        5. 导出代理
+        6. 清理无效代理
+        """
+        # 1. 获取初始统计
+        response = await client.get("/api/proxies/stats")
+        assert response.status_code == 200
+        initial_stats = response.json()["data"]
+        
+        # 2. 列出代理
+        response = await client.post("/api/proxies", json={
+            "page": 1,
+            "page_size": 20,
+        })
+        assert response.status_code == 200
+        
+        # 3. 触发所有插件爬取
+        response = await client.post("/api/plugins/crawl-all")
+        assert response.status_code == 200
+        crawl_result = response.json()["data"]
+        
+        # 4. 获取更新后的统计
+        response = await client.get("/api/proxies/stats")
+        updated_stats = response.json()["data"]
+        
+        # 5. 导出代理（所有格式）
+        for fmt in ["csv", "txt", "json"]:
+            response = await client.get(f"/api/proxies/export/{fmt}")
+            assert response.status_code == 200
+        
+        # 6. 清理无效代理
+        response = await client.delete("/api/proxies/clean-invalid")
+        assert response.status_code == 200
+
+    @pytest.mark.asyncio
+    async def test_plugin_management_workflow(self, client):
+        """测试插件管理完整工作流
+        
+        场景：
+        1. 列出所有插件
+        2. 禁用某个插件
+        3. 更新插件配置
+        4. 启用插件
+        5. 触发单个插件爬取
+        """
+        # 1. 列出插件
+        response = await client.get("/api/plugins")
+        assert response.status_code == 200
+        plugins = response.json()["data"]["plugins"]
+        
+        if not plugins:
+            pytest.skip("没有可用的插件")
+        
+        plugin_id = plugins[0]["id"]
+        
+        # 2. 禁用插件
+        response = await client.put(f"/api/plugins/{plugin_id}/toggle", json={"enabled": False})
+        assert response.status_code == 200
+        
+        # 3. 获取插件配置
+        response = await client.get(f"/api/plugins/{plugin_id}/config")
+        assert response.status_code == 200
+        
+        # 4. 更新插件配置
+        response = await client.post(
+            f"/api/plugins/{plugin_id}/config",
+            json={"config": {"max_pages": 3}}
+        )
+        assert response.status_code == 200
+        
+        # 5. 启用插件
+        response = await client.put(f"/api/plugins/{plugin_id}/toggle", json={"enabled": True})
+        assert response.status_code == 200
+        
+        # 6. 触发爬取
+        response = await client.post(f"/api/plugins/{plugin_id}/crawl")
+        assert response.status_code == 200
+
+    @pytest.mark.asyncio
+    async def test_scheduler_workflow(self, client):
+        """测试调度器工作流
+        
+        场景：
+        1. 启动调度器
+        2. 触发立即验证
+        3. 检查状态
+        4. 停止调度器
+        """
+        # 1. 启动调度器
+        response = await client.post("/api/scheduler/start")
+        assert response.status_code == 200
+        
+        # 2. 触发立即验证
+        response = await client.post("/api/scheduler/validate-now")
+        assert response.status_code == 200
+        
+        # 3. 检查状态
+        response = await client.get("/api/scheduler/status")
+        assert response.status_code == 200
+        assert response.json()["data"]["running"] is True
+        
+        # 4. 停止调度器
+        response = await client.post("/api/scheduler/stop")
+        assert response.status_code == 200
+        assert response.json()["data"]["running"] is False
+
+    @pytest.mark.asyncio
+    async def test_settings_workflow(self, client):
+        """测试设置工作流
+        
+        场景：
+        1. 获取当前设置
+        2. 修改设置
+        3. 验证设置已保存
+        4. 恢复默认设置
+        """
+        # 1. 获取当前设置
+        response = await client.get("/api/settings")
+        assert response.status_code == 200
+        original_settings = response.json()["data"]
+        
+        # 2. 修改设置
+        new_settings = original_settings.copy()
+        new_settings["crawl_timeout"] = 45
+        new_settings["auto_validate"] = not original_settings["auto_validate"]
+        
+        response = await client.post("/api/settings", json=new_settings)
+        assert response.status_code == 200
+        
+        # 3. 验证设置已保存
+        response = await client.get("/api/settings")
+        saved_settings = response.json()["data"]
+        assert saved_settings["crawl_timeout"] == 45
+        
+        # 4. 恢复原始设置
+        response = await client.post("/api/settings", json=original_settings)
+        assert response.status_code == 200
+
+    @pytest.mark.asyncio
+    async def test_batch_operations_workflow(self, client):
+        """测试批量操作工作流
+        
+        场景：
+        1. 批量删除不存在的代理（幂等性测试）
+        2. 导出所有代理
+        3. 获取随机代理
+        """
+        # 1. 批量删除（幂等性）
+        response = await client.post("/api/proxies/batch-delete", json={
+            "proxies": [
+                {"ip": "192.168.100.1", "port": 8080},
+                {"ip": "192.168.100.2", "port": 8081},
+            ]
+        })
+        assert response.status_code == 200
+        
+        # 2. 导出所有格式
+        for fmt in ["csv", "txt", "json"]:
+            response = await client.get(f"/api/proxies/export/{fmt}")
+            assert response.status_code == 200
+        
+        # 3. 获取随机代理（可能返回 200 或 404）
+        response = await client.get("/api/proxies/random")
+        assert response.status_code in [200, 404]