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/repositories/task_repo.py

@@ -0,0 +1,135 @@
+"""验证任务队列持久化层"""
+import aiosqlite
+from typing import List, Optional
+from app.models.domain import ProxyRaw
+from app.core.log import logger
+
+
+class ValidationTaskRepository:
+    """验证任务 Repository —— 支持队列持久化"""
+
+    @staticmethod
+    async def insert_batch(db: aiosqlite.Connection, proxies: List[ProxyRaw]) -> int:
+        if not proxies:
+            return 0
+        try:
+            rows = [(p.ip, p.port, p.protocol) for p in proxies]
+            await db.executemany(
+                """
+                INSERT INTO validation_tasks (ip, port, protocol, status, created_at)
+                VALUES (?, ?, ?, 'pending', CURRENT_TIMESTAMP)
+                """,
+                rows,
+            )
+            await db.commit()
+            return len(rows)
+        except Exception as e:
+            logger.error(f"insert_batch validation tasks failed: {e}")
+            return 0
+
+    @staticmethod
+    async def acquire_pending(db: aiosqlite.Connection) -> Optional[dict]:
+        """原子性地获取一个 pending 任务并将其标记为 processing"""
+        try:
+            async with db.execute(
+                """
+                SELECT id, ip, port, protocol FROM validation_tasks
+                WHERE status = 'pending'
+                ORDER BY id ASC
+                LIMIT 1
+                """
+            ) as cursor:
+                row = await cursor.fetchone()
+                if not row:
+                    return None
+                task_id = row[0]
+                await db.execute(
+                    "UPDATE validation_tasks SET status = 'processing', updated_at = CURRENT_TIMESTAMP WHERE id = ?",
+                    (task_id,),
+                )
+                await db.commit()
+                return {"id": task_id, "ip": row[1], "port": row[2], "protocol": row[3]}
+        except Exception as e:
+            logger.error(f"acquire_pending failed: {e}")
+            return None
+
+    @staticmethod
+    async def complete_task(
+        db: aiosqlite.Connection,
+        task_id: int,
+        is_valid: bool,
+        response_time_ms: Optional[float] = None,
+    ) -> bool:
+        try:
+            await db.execute(
+                """
+                UPDATE validation_tasks
+                SET status = 'completed',
+                    result = ?,
+                    response_time_ms = ?,
+                    updated_at = CURRENT_TIMESTAMP
+                WHERE id = ?
+                """,
+                ("valid" if is_valid else "invalid", response_time_ms, task_id),
+            )
+            await db.commit()
+            return True
+        except Exception as e:
+            logger.error(f"complete_task failed: {e}")
+            return False
+
+    @staticmethod
+    async def fail_task(db: aiosqlite.Connection, task_id: int) -> bool:
+        try:
+            await db.execute(
+                """
+                UPDATE validation_tasks
+                SET status = 'failed',
+                    result = 'invalid',
+                    updated_at = CURRENT_TIMESTAMP
+                WHERE id = ?
+                """,
+                (task_id,),
+            )
+            await db.commit()
+            return True
+        except Exception as e:
+            logger.error(f"fail_task failed: {e}")
+            return False
+
+    @staticmethod
+    async def get_pending_count(db: aiosqlite.Connection) -> int:
+        async with db.execute(
+            "SELECT COUNT(*) FROM validation_tasks WHERE status = 'pending'"
+        ) as cursor:
+            row = await cursor.fetchone()
+            return row[0] if row else 0
+
+    @staticmethod
+    async def reset_processing(db: aiosqlite.Connection) -> int:
+        """将异常中断的 processing 任务重置为 pending，用于启动恢复"""
+        try:
+            await db.execute(
+                """
+                UPDATE validation_tasks
+                SET status = 'pending', updated_at = CURRENT_TIMESTAMP
+                WHERE status = 'processing'
+                """
+            )
+            await db.commit()
+            return db.total_changes
+        except Exception as e:
+            logger.error(f"reset_processing failed: {e}")
+            return 0
+
+    @staticmethod
+    async def cleanup_old(db: aiosqlite.Connection, days: int = 7) -> int:
+        try:
+            await db.execute(
+                "DELETE FROM validation_tasks WHERE updated_at < datetime('now', '-{} days')".format(days)
+            )
+            await db.commit()
+            return db.total_changes
+        except Exception as e:
+            logger.error(f"cleanup_old tasks failed: {e}")
+            return 0