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/validator_service.py

@@ -0,0 +1,103 @@
+"""代理验证服务 - 支持 HTTP/HTTPS/SOCKS4/SOCKS5"""
+import asyncio
+import random
+import time
+import aiohttp
+import aiohttp_socks
+from typing import Tuple
+from core.log import logger
+
+
+class ValidatorService:
+    """代理验证器"""
+
+    def __init__(
+        self,
+        timeout: float = 5.0,
+        connect_timeout: float = 3.0,
+        max_concurrency: int = 50,
+    ):
+        self.timeout = timeout
+        self.connect_timeout = connect_timeout
+        self.semaphore = asyncio.Semaphore(max_concurrency)
+        self.http_sources = [
+            "http://httpbin.org/ip",
+            "http://api.ipify.org",
+        ]
+        self.https_sources = [
+            "https://httpbin.org/ip",
+            "https://api.ipify.org",
+        ]
+
+    def _get_test_url(self, protocol: str) -> str:
+        protocol = protocol.lower()
+        if protocol == "https":
+            return random.choice(self.https_sources)
+        return random.choice(self.http_sources)
+
+    async def validate(self, ip: str, port: int, protocol: str = "http") -> Tuple[bool, float]:
+        """验证单个代理，返回 (是否有效, 延迟毫秒)"""
+        protocol = protocol.lower()
+        test_url = self._get_test_url(protocol)
+
+        async with self.semaphore:
+            start = time.time()
+            try:
+                if protocol in ("socks4", "socks5"):
+                    return await self._validate_socks(ip, port, protocol, test_url, start)
+                else:
+                    return await self._validate_http(ip, port, protocol, test_url, start)
+            except asyncio.TimeoutError:
+                logger.debug(f"Validation timeout: {ip}:{port} ({protocol})")
+                return False, 0.0
+            except Exception as e:
+                logger.debug(f"Validation error {ip}:{port} ({protocol}): {e}")
+                return False, 0.0
+
+    async def _validate_http(
+        self, ip: str, port: int, protocol: str, test_url: str, start: float
+    ) -> Tuple[bool, float]:
+        proxy_url = f"http://{ip}:{port}"
+        connector = aiohttp.TCPConnector(ssl=False, limit=0, force_close=True)
+        timeout = aiohttp.ClientTimeout(total=self.timeout, connect=self.connect_timeout)
+
+        try:
+            async with aiohttp.ClientSession(connector=connector, timeout=timeout) as session:
+                async with session.get(
+                    test_url, proxy=proxy_url, allow_redirects=True
+                ) as response:
+                    if response.status in (200, 301, 302):
+                        latency = round((time.time() - start) * 1000, 2)
+                        logger.info(f"HTTP valid: {ip}:{port} ({protocol}) {latency}ms")
+                        return True, latency
+                    return False, 0.0
+        finally:
+            await connector.close()
+
+    async def _validate_socks(
+        self, ip: str, port: int, protocol: str, test_url: str, start: float
+    ) -> Tuple[bool, float]:
+        proxy_type = (
+            aiohttp_socks.ProxyType.SOCKS4
+            if protocol == "socks4"
+            else aiohttp_socks.ProxyType.SOCKS5
+        )
+        connector = aiohttp_socks.ProxyConnector(
+            proxy_type=proxy_type,
+            host=ip,
+            port=port,
+            rdns=True,
+            ssl=False,
+        )
+        timeout = aiohttp.ClientTimeout(total=self.timeout, connect=self.connect_timeout)
+
+        try:
+            async with aiohttp.ClientSession(connector=connector, timeout=timeout) as session:
+                async with session.get(test_url, allow_redirects=True) as response:
+                    if response.status in (200, 301, 302):
+                        latency = round((time.time() - start) * 1000, 2)
+                        logger.info(f"SOCKS valid: {ip}:{port} ({protocol}) {latency}ms")
+                        return True, latency
+                    return False, 0.0
+        finally:
+            await connector.close()