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/settings_repo.py

@@ -0,0 +1,140 @@
+"""设置数据访问层"""
+import json
+import aiosqlite
+from typing import Optional, Dict, Any
+from app.core.log import logger
+
+
+DEFAULT_SETTINGS = {
+    "crawl_timeout": 30,
+    "validation_timeout": 10,
+    "max_retries": 3,
+    "default_concurrency": 50,
+    "min_proxy_score": 0,
+    "proxy_expiry_days": 7,
+    "auto_validate": True,
+    "validate_interval_minutes": 30,
+}
+
+
+class SettingsRepository:
+    """系统设置 Repository"""
+
+    @staticmethod
+    async def get_all(db: aiosqlite.Connection) -> Dict[str, Any]:
+        settings = DEFAULT_SETTINGS.copy()
+        try:
+            async with db.execute("SELECT key, value FROM settings") as cursor:
+                rows = await cursor.fetchall()
+                for key, value in rows:
+                    # 类型转换
+                    default = DEFAULT_SETTINGS.get(key)
+                    if isinstance(default, bool):
+                        settings[key] = value.lower() == "true"
+                    elif isinstance(default, int):
+                        settings[key] = int(value)
+                    else:
+                        settings[key] = value
+        except Exception as e:
+            logger.error(f"get_all settings failed: {e}")
+        return settings
+
+    @staticmethod
+    async def save(db: aiosqlite.Connection, settings: Dict[str, Any]) -> bool:
+        try:
+            for key, value in settings.items():
+                await db.execute(
+                    """
+                    INSERT INTO settings (key, value, updated_at)
+                    VALUES (?, ?, CURRENT_TIMESTAMP)
+                    ON CONFLICT(key) DO UPDATE SET
+                        value = excluded.value,
+                        updated_at = CURRENT_TIMESTAMP
+                    """,
+                    (key, str(value)),
+                )
+            await db.commit()
+            return True
+        except Exception as e:
+            logger.error(f"save settings failed: {e}")
+            return False
+
+
+class PluginSettingsRepository:
+    """插件设置 Repository"""
+
+    @staticmethod
+    async def get_enabled(db: aiosqlite.Connection, plugin_id: str) -> Optional[bool]:
+        async with db.execute(
+            "SELECT enabled FROM plugin_settings WHERE plugin_id = ?", (plugin_id,)
+        ) as cursor:
+            row = await cursor.fetchone()
+            if row:
+                return bool(row[0])
+            return None
+
+    @staticmethod
+    async def set_enabled(db: aiosqlite.Connection, plugin_id: str, enabled: bool) -> bool:
+        try:
+            await db.execute(
+                """
+                INSERT INTO plugin_settings (plugin_id, enabled, created_at, updated_at)
+                VALUES (?, ?, CURRENT_TIMESTAMP, CURRENT_TIMESTAMP)
+                ON CONFLICT(plugin_id) DO UPDATE SET
+                    enabled = excluded.enabled,
+                    updated_at = CURRENT_TIMESTAMP
+                """,
+                (plugin_id, int(enabled)),
+            )
+            await db.commit()
+            return True
+        except Exception as e:
+            logger.error(f"set_enabled failed for {plugin_id}: {e}")
+            return False
+
+    @staticmethod
+    async def get_config(db: aiosqlite.Connection, plugin_id: str) -> Optional[Dict[str, Any]]:
+        async with db.execute(
+            "SELECT config_json FROM plugin_settings WHERE plugin_id = ?", (plugin_id,)
+        ) as cursor:
+            row = await cursor.fetchone()
+            if row and row[0]:
+                try:
+                    return json.loads(row[0])
+                except json.JSONDecodeError:
+                    return None
+            return None
+
+    @staticmethod
+    async def set_config(db: aiosqlite.Connection, plugin_id: str, config: Dict[str, Any]) -> bool:
+        try:
+            await db.execute(
+                """
+                INSERT INTO plugin_settings (plugin_id, config_json, updated_at)
+                VALUES (?, ?, CURRENT_TIMESTAMP)
+                ON CONFLICT(plugin_id) DO UPDATE SET
+                    config_json = excluded.config_json,
+                    updated_at = CURRENT_TIMESTAMP
+                """,
+                (plugin_id, json.dumps(config, ensure_ascii=False)),
+            )
+            await db.commit()
+            return True
+        except Exception as e:
+            logger.error(f"set_config failed for {plugin_id}: {e}")
+            return False
+
+    @staticmethod
+    async def list_all(db: aiosqlite.Connection) -> Dict[str, Dict[str, Any]]:
+        result = {}
+        async with db.execute("SELECT plugin_id, enabled, config_json FROM plugin_settings") as cursor:
+            rows = await cursor.fetchall()
+            for plugin_id, enabled, config_json in rows:
+                config = {}
+                if config_json:
+                    try:
+                        config = json.loads(config_json)
+                    except json.JSONDecodeError:
+                        pass
+                result[plugin_id] = {"enabled": bool(enabled), "config": config}
+        return result