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/plugin_service.py

@@ -0,0 +1,139 @@
+"""插件业务服务"""
+from datetime import datetime
+from typing import List, Optional
+from app.core.db import get_db
+from app.core.plugin_system.registry import registry
+from app.core.plugin_system.base import BaseCrawlerPlugin
+from app.repositories.settings_repo import PluginSettingsRepository
+from app.models.domain import PluginInfo, ProxyRaw
+from app.core.log import logger
+
+
+class PluginService:
+    """插件业务服务：管理插件生命周期、执行爬取、配置管理"""
+
+    def __init__(self):
+        self.plugin_settings_repo = PluginSettingsRepository()
+        self._stats: dict[str, dict] = {}
+
+    async def list_plugins(self) -> List[PluginInfo]:
+        """获取所有插件信息（合并持久化状态和配置）"""
+        async with get_db() as db:
+            db_states = await self.plugin_settings_repo.list_all(db)
+
+        result = []
+        for plugin in registry.list_plugins():
+            # 合并持久化状态
+            state = db_states.get(plugin.name, {})
+            if "enabled" in state:
+                plugin.enabled = state["enabled"]
+            if "config" in state and isinstance(state["config"], dict):
+                plugin.update_config(state["config"])
+
+            stat = self._stats.get(plugin.name, {
+                "success_count": 0,
+                "failure_count": 0,
+                "last_run": None,
+            })
+            result.append(PluginInfo(
+                id=plugin.name,
+                name=plugin.name,
+                display_name=plugin.display_name or plugin.name,
+                description=plugin.description or f"从 {plugin.name} 爬取代理",
+                enabled=plugin.enabled,
+                last_run=stat.get("last_run"),
+                success_count=stat.get("success_count", 0),
+                failure_count=stat.get("failure_count", 0),
+            ))
+        return result
+
+    async def toggle_plugin(self, plugin_id: str, enabled: bool) -> bool:
+        plugin = registry.get(plugin_id)
+        if not plugin:
+            return False
+        async with get_db() as db:
+            success = await self.plugin_settings_repo.set_enabled(db, plugin_id, enabled)
+        if success:
+            plugin.enabled = enabled
+            logger.info(f"Plugin {plugin_id} toggled to {enabled}")
+        return success
+
+    async def get_plugin_config(self, plugin_id: str) -> Optional[dict]:
+        """获取插件当前配置（合并默认值和持久化值）"""
+        plugin = registry.get(plugin_id)
+        if not plugin:
+            return None
+        async with get_db() as db:
+            saved = await self.plugin_settings_repo.get_config(db, plugin_id)
+        config = dict(plugin.default_config)
+        if saved:
+            config.update(saved)
+        return config
+
+    async def update_plugin_config(self, plugin_id: str, config: dict) -> bool:
+        """更新插件配置（只保存已存在于 default_config 中的键）"""
+        plugin = registry.get(plugin_id)
+        if not plugin:
+            return False
+        # 过滤非法键
+        safe_config = {k: v for k, v in config.items() if k in plugin.default_config}
+        if not safe_config:
+            return False
+        plugin.update_config(safe_config)
+        async with get_db() as db:
+            return await self.plugin_settings_repo.set_config(db, plugin_id, plugin.config)
+
+    def get_plugin(self, plugin_id: str) -> Optional[BaseCrawlerPlugin]:
+        return registry.get(plugin_id)
+
+    async def run_plugin(self, plugin_id: str) -> List[ProxyRaw]:
+        """执行单个插件爬取"""
+        plugin = self.get_plugin(plugin_id)
+        if not plugin:
+            raise ValueError(f"Plugin {plugin_id} not found")
+        if not plugin.enabled:
+            logger.warning(f"Plugin {plugin_id} is disabled, skip crawl")
+            return []
+
+        try:
+            results = await plugin.crawl()
+            self._record_stat(plugin_id, success=len(results))
+            logger.info(f"Plugin {plugin_id} crawled {len(results)} proxies")
+            return results
+        except Exception as e:
+            self._record_stat(plugin_id, failure=1)
+            logger.error(f"Plugin {plugin_id} crawl failed: {e}")
+            return []
+
+    async def run_all_plugins(self) -> List[ProxyRaw]:
+        """执行所有启用插件的爬取"""
+        all_results: List[ProxyRaw] = []
+        for plugin in registry.list_plugins():
+            if not plugin.enabled:
+                continue
+            try:
+                results = await self.run_plugin(plugin.name)
+                all_results.extend(results)
+            except Exception as e:
+                logger.error(f"Run all plugins error at {plugin.name}: {e}")
+        # 去重
+        seen = set()
+        unique = []
+        for p in all_results:
+            key = (p.ip, p.port, p.protocol)
+            if key not in seen:
+                seen.add(key)
+                unique.append(p)
+        return unique
+
+    def _record_stat(self, plugin_id: str, success: int = 0, failure: int = 0):
+        if plugin_id not in self._stats:
+            self._stats[plugin_id] = {
+                "success_count": 0,
+                "failure_count": 0,
+                "last_run": None,
+            }
+        self._stats[plugin_id]["success_count"] += success
+        self._stats[plugin_id]["failure_count"] += failure
+        if success or failure:
+            self._stats[plugin_id]["last_run"] = datetime.now()