全面架构重构：建立分层架构与高度可扩展的插件系统

后端重构：
- 新增分层架构：API Routes -> Services -> Repositories -> Infrastructure
- 彻底移除全局单例，全面采用 FastAPI 依赖注入
- 新增 api/ 目录拆分路由（proxies, plugins, scheduler, settings, stats）
- 新增 services/ 业务逻辑层：ProxyService, PluginService, SchedulerService, ValidatorService, SettingsService
- 新增 repositories/ 数据访问层：ProxyRepository, SettingsRepository, PluginSettingsRepository
- 新增 models/ 层：Pydantic Schemas + Domain Models
- 重写 core/config.py：采用 Pydantic Settings 管理配置
- 新增 core/db.py：基于 asynccontextmanager 的连接管理，支持数据库迁移
- 新增 core/exceptions.py：统一业务异常体系

插件系统重构（核心）：
- 新增 core/plugin_system/：BaseCrawlerPlugin + PluginRegistry
- 采用显式注册模式（装饰器 + plugins/__init__.py），类型安全、测试友好
- 新增 plugins/base.py：BaseHTTPPlugin 通用 HTTP 爬虫基类
- 迁移全部 7 个插件到新架构（fate0, proxylist_download, ip3366, ip89, kuaidaili, speedx, yundaili）
- 插件状态持久化到 plugin_settings 表

任务调度重构：
- 新增 core/tasks/queue.py：ValidationQueue + WorkerPool
- 解耦爬取与验证：爬虫只负责爬取，代理提交队列后由 Worker 异步验证
- 调度器定时从数据库拉取存量代理并分批投入验证队列

前端调整：
- 新增 frontend/src/services/ 层拆分 API 调用逻辑
- 调整 stores/ 和 views/ 使用 Service 层
- 保持 API 兼容性，页面无需大幅修改

其他：
- 新增 main.py 作为新入口
- 新增 DESIGN.md 架构设计文档
- 更新 requirements.txt 增加 pydantic-settings

services/plugin_service.py

@@ -0,0 +1,111 @@
+"""插件业务服务"""
+from datetime import datetime
+from typing import List, Optional
+from core.db import get_db
+from core.plugin_system.registry import registry
+from core.plugin_system.base import BaseCrawlerPlugin
+from repositories.settings_repo import PluginSettingsRepository
+from models.domain import PluginInfo, ProxyRaw
+from core.log import logger
+
+
+class PluginService:
+    """插件业务服务：管理插件生命周期、执行爬取"""
+
+    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）"""
+        async with get_db() as db:
+            db_states = await self.plugin_settings_repo.list_all(db)
+
+        result = []
+        for plugin in registry.list_plugins():
+            # 如果有持久化状态，覆盖内存状态
+            if plugin.name in db_states:
+                plugin.enabled = db_states[plugin.name]
+
+            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
+
+    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()