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/integration/test_scheduler_api.py

@@ -0,0 +1,101 @@
+"""调度器 API 集成测试 - 测试 /api/scheduler/* 所有接口"""
+import pytest
+
+
+class TestSchedulerAPI:
+    """测试调度器相关 API"""
+
+    @pytest.mark.asyncio
+    async def test_get_scheduler_status(self, client):
+        """测试 GET /api/scheduler/status"""
+        response = await client.get("/api/scheduler/status")
+        assert response.status_code == 200
+        data = response.json()
+        assert data["code"] == 200
+        assert "running" in data["data"]
+        assert "interval_minutes" in data["data"]
+        assert isinstance(data["data"]["running"], bool)
+
+    @pytest.mark.asyncio
+    async def test_start_scheduler(self, client):
+        """测试 POST /api/scheduler/start"""
+        response = await client.post("/api/scheduler/start")
+        assert response.status_code == 200
+        data = response.json()
+        assert data["code"] == 200
+        assert data["data"]["running"] is True
+
+    @pytest.mark.asyncio
+    async def test_start_scheduler_already_running(self, client):
+        """测试 POST /api/scheduler/start - 已经运行"""
+        # 先启动
+        await client.post("/api/scheduler/start")
+        # 再次启动
+        response = await client.post("/api/scheduler/start")
+        assert response.status_code == 200
+        data = response.json()
+        assert data["code"] == 200
+        assert "已在运行" in data["message"] or data["data"]["running"] is True
+
+    @pytest.mark.asyncio
+    async def test_stop_scheduler(self, client):
+        """测试 POST /api/scheduler/stop"""
+        # 先确保调度器在运行
+        await client.post("/api/scheduler/start")
+        
+        response = await client.post("/api/scheduler/stop")
+        assert response.status_code == 200
+        data = response.json()
+        assert data["code"] == 200
+        assert data["data"]["running"] is False
+
+    @pytest.mark.asyncio
+    async def test_stop_scheduler_already_stopped(self, client):
+        """测试 POST /api/scheduler/stop - 已经停止"""
+        # 先停止
+        await client.post("/api/scheduler/stop")
+        # 再次停止
+        response = await client.post("/api/scheduler/stop")
+        assert response.status_code == 200
+        data = response.json()
+        assert data["code"] == 200
+        assert "未运行" in data["message"] or data["data"]["running"] is False
+
+    @pytest.mark.asyncio
+    async def test_validate_now(self, client):
+        """测试 POST /api/scheduler/validate-now"""
+        # 先启动调度器
+        await client.post("/api/scheduler/start")
+        
+        response = await client.post("/api/scheduler/validate-now")
+        assert response.status_code == 200
+        data = response.json()
+        assert data["code"] == 200
+        assert data["data"]["started"] is True
+
+    @pytest.mark.asyncio
+    async def test_scheduler_full_workflow(self, client):
+        """测试调度器完整工作流"""
+        # 1. 获取初始状态
+        response = await client.get("/api/scheduler/status")
+        initial_status = response.json()["data"]
+        
+        # 2. 启动调度器
+        response = await client.post("/api/scheduler/start")
+        assert response.json()["data"]["running"] is True
+        
+        # 3. 验证状态
+        response = await client.get("/api/scheduler/status")
+        assert response.json()["data"]["running"] is True
+        
+        # 4. 触发立即验证
+        response = await client.post("/api/scheduler/validate-now")
+        assert response.json()["data"]["started"] is True
+        
+        # 5. 停止调度器
+        response = await client.post("/api/scheduler/stop")
+        assert response.json()["data"]["running"] is False
+        
+        # 6. 验证最终状态
+        response = await client.get("/api/scheduler/status")
+        assert response.json()["data"]["running"] is False