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/core/db.py

@@ -0,0 +1,120 @@
+"""数据库连接管理 - 使用上下文管理器，避免全局单例连接泄漏"""
+import os
+import aiosqlite
+from contextlib import asynccontextmanager
+from typing import AsyncIterator
+from app.core.config import settings
+from app.core.log import logger
+
+
+DB_PATH = os.path.join(settings.base_dir, settings.db_path)
+
+
+def ensure_db_dir():
+    db_dir = os.path.dirname(DB_PATH)
+    if db_dir and not os.path.exists(db_dir):
+        os.makedirs(db_dir, exist_ok=True)
+
+
+async def init_db():
+    """初始化数据库表结构（支持迁移）"""
+    ensure_db_dir()
+    async with aiosqlite.connect(DB_PATH) as db:
+        await db.execute("PRAGMA journal_mode=WAL")
+        await db.execute("PRAGMA synchronous=NORMAL")
+        await db.execute("PRAGMA cache_size=-64000")
+        await db.execute("PRAGMA temp_store=MEMORY")
+
+        await db.execute("""
+            CREATE TABLE IF NOT EXISTS proxies (
+                id INTEGER PRIMARY KEY AUTOINCREMENT,
+                ip TEXT NOT NULL,
+                port INTEGER NOT NULL,
+                protocol TEXT DEFAULT 'http',
+                score INTEGER DEFAULT 10,
+                response_time_ms REAL,
+                last_check TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
+                created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
+                UNIQUE(ip, port)
+            )
+        """)
+
+        # 迁移：如果旧表缺少 response_time_ms 列，则添加
+        try:
+            await db.execute("SELECT response_time_ms FROM proxies LIMIT 1")
+        except Exception:
+            await db.execute("ALTER TABLE proxies ADD COLUMN response_time_ms REAL")
+            logger.info("Migrated: added response_time_ms column")
+
+        # 迁移：如果旧表缺少 created_at 列，则添加
+        try:
+            await db.execute("SELECT created_at FROM proxies LIMIT 1")
+        except Exception:
+            await db.execute("ALTER TABLE proxies ADD COLUMN created_at TIMESTAMP")
+            await db.execute("UPDATE proxies SET created_at = CURRENT_TIMESTAMP WHERE created_at IS NULL")
+            logger.info("Migrated: added created_at column")
+
+        await db.execute("CREATE INDEX IF NOT EXISTS idx_score ON proxies(score)")
+        await db.execute("CREATE INDEX IF NOT EXISTS idx_protocol ON proxies(protocol)")
+        await db.execute("CREATE INDEX IF NOT EXISTS idx_last_check ON proxies(last_check)")
+        await db.execute("CREATE INDEX IF NOT EXISTS idx_ip_port ON proxies(ip, port)")
+
+        # 插件设置表
+        await db.execute("""
+            CREATE TABLE IF NOT EXISTS plugin_settings (
+                plugin_id TEXT PRIMARY KEY,
+                enabled INTEGER DEFAULT 1,
+                config_json TEXT DEFAULT '{}',
+                created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
+                updated_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
+            )
+        """)
+
+        # 迁移：为旧版 plugin_settings 表增加 config_json 列
+        try:
+            await db.execute("SELECT config_json FROM plugin_settings LIMIT 1")
+        except Exception:
+            await db.execute("ALTER TABLE plugin_settings ADD COLUMN config_json TEXT DEFAULT '{}'")
+            logger.info("Migrated: added config_json column to plugin_settings")
+
+        # 验证任务队列表
+        await db.execute("""
+            CREATE TABLE IF NOT EXISTS validation_tasks (
+                id INTEGER PRIMARY KEY AUTOINCREMENT,
+                ip TEXT NOT NULL,
+                port INTEGER NOT NULL,
+                protocol TEXT DEFAULT 'http',
+                status TEXT DEFAULT 'pending',
+                result TEXT,
+                response_time_ms REAL,
+                created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
+                updated_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
+            )
+        """)
+        await db.execute("CREATE INDEX IF NOT EXISTS idx_validation_status ON validation_tasks(status)")
+        await db.execute("CREATE INDEX IF NOT EXISTS idx_validation_created ON validation_tasks(created_at)")
+
+        # 系统设置表
+        await db.execute("""
+            CREATE TABLE IF NOT EXISTS settings (
+                key TEXT PRIMARY KEY,
+                value TEXT NOT NULL,
+                updated_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
+            )
+        """)
+
+        await db.commit()
+    logger.info("Database initialized")
+
+
+@asynccontextmanager
+async def get_db() -> AsyncIterator[aiosqlite.Connection]:
+    """获取数据库连接的异步上下文管理器"""
+    ensure_db_dir()
+    db = await aiosqlite.connect(DB_PATH)
+    try:
+        await db.execute("PRAGMA journal_mode=WAL")
+        await db.execute("PRAGMA synchronous=NORMAL")
+        yield db
+    finally:
+        await db.close()