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/services/scheduler_service.py

@@ -0,0 +1,88 @@
+"""调度器服务 - 定时验证存量代理"""
+import asyncio
+from datetime import datetime
+from app.core.db import get_db
+from app.repositories.proxy_repo import ProxyRepository
+from app.core.tasks.queue import ValidationQueue
+from app.core.config import settings as app_settings
+from app.core.log import logger
+
+
+class SchedulerService:
+    """代理验证调度器"""
+
+    def __init__(
+        self,
+        validation_queue: ValidationQueue,
+        proxy_repo: ProxyRepository = ProxyRepository(),
+    ):
+        self.validation_queue = validation_queue
+        self.proxy_repo = proxy_repo
+        self.interval_minutes = 30
+        self.running = False
+        self._task: asyncio.Task | None = None
+
+    async def start(self):
+        if self.running:
+            logger.warning("Scheduler already running")
+            return
+        self.running = True
+        await self.validation_queue.start()
+        self._task = asyncio.create_task(self._run_loop())
+        logger.info("Scheduler started")
+
+    async def stop(self):
+        self.running = False
+        if self._task:
+            self._task.cancel()
+            try:
+                await self._task
+            except asyncio.CancelledError:
+                pass
+            self._task = None
+        await self.validation_queue.stop()
+        logger.info("Scheduler stopped")
+
+    async def validate_all_now(self):
+        """立即执行一次全量验证（后台运行，不阻塞）"""
+        asyncio.create_task(self._do_validate_all())
+
+    async def _run_loop(self):
+        """定时循环"""
+        while self.running:
+            try:
+                await self._do_validate_all()
+            except Exception as e:
+                logger.error(f"Scheduler loop error: {e}")
+            # 等待下一次
+            for _ in range(self.interval_minutes * 60):
+                if not self.running:
+                    break
+                await asyncio.sleep(1)
+
+    async def _do_validate_all(self):
+        """验证数据库中所有存量代理"""
+        logger.info("Starting scheduled validation for all proxies")
+        async with get_db() as db:
+            proxies = await self.proxy_repo.list_all(db)
+        if not proxies:
+            logger.info("No proxies to validate")
+            return
+
+        logger.info(f"Validating {len(proxies)} proxies from database")
+        from app.models.domain import ProxyRaw
+
+        # 批量提交到验证队列
+        batch_size = 100
+        for i in range(0, len(proxies), batch_size):
+            if not self.running:
+                break
+            batch = proxies[i : i + batch_size]
+            await self.validation_queue.submit([
+                ProxyRaw(p.ip, p.port, p.protocol) for p in batch
+            ])
+            # 等待当前批次处理完
+            await self.validation_queue.drain()
+            logger.info(f"Validated batch {i//batch_size + 1}/{(len(proxies)-1)//batch_size + 1}")
+
+        logger.info("Scheduled validation completed")