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

models/schemas.py

@@ -0,0 +1,105 @@
+"""Pydantic 模型 - 用于 API 请求/响应校验"""
+from pydantic import BaseModel, Field, field_validator
+from typing import Optional, List
+
+
+class ProxyCreate(BaseModel):
+    ip: str
+    port: int = Field(ge=1, le=65535)
+    protocol: str = "http"
+    score: int = Field(default=10, ge=0, le=100)
+
+    @field_validator("protocol")
+    @classmethod
+    def validate_protocol(cls, v: str):
+        v = v.lower().strip()
+        if v not in ("http", "https", "socks4", "socks5"):
+            raise ValueError("protocol must be http, https, socks4 or socks5")
+        return v
+
+
+class ProxyResponse(BaseModel):
+    ip: str
+    port: int
+    protocol: str
+    score: int
+    last_check: Optional[str] = None
+
+
+class PluginResponse(BaseModel):
+    id: str
+    name: str
+    display_name: str
+    description: str
+    enabled: bool
+    last_run: Optional[str] = None
+    success_count: int = 0
+    failure_count: int = 0
+
+
+class SettingsSchema(BaseModel):
+    crawl_timeout: int = Field(default=30, ge=5, le=120)
+    validation_timeout: int = Field(default=10, ge=3, le=60)
+    max_retries: int = Field(default=3, ge=0, le=10)
+    default_concurrency: int = Field(default=50, ge=10, le=200)
+    min_proxy_score: int = Field(default=0, ge=0, le=100)
+    proxy_expiry_days: int = Field(default=7, ge=1, le=30)
+    auto_validate: bool = True
+    validate_interval_minutes: int = Field(default=30, ge=5, le=1440)
+
+
+class CrawlResult(BaseModel):
+    plugin_id: str
+    proxy_count: int
+    valid_count: int
+    invalid_count: int = 0
+
+
+class ProxyListRequest(BaseModel):
+    page: int = Field(default=1, ge=1)
+    page_size: int = Field(default=20, ge=1, le=100)
+    protocol: Optional[str] = None
+    min_score: int = Field(default=0, ge=0)
+    max_score: Optional[int] = Field(default=None, ge=0)
+    sort_by: str = "last_check"
+    sort_order: str = "DESC"
+
+    @field_validator("protocol")
+    @classmethod
+    def validate_protocol(cls, v):
+        if v is not None and v.lower() not in ("http", "https", "socks4", "socks5"):
+            raise ValueError("协议类型必须是 http, https, socks4 或 socks5")
+        return v.lower() if v else v
+
+    @field_validator("sort_by")
+    @classmethod
+    def validate_sort_by(cls, v):
+        if v not in ("ip", "port", "protocol", "score", "last_check"):
+            raise ValueError("排序字段必须是 ip, port, protocol, score 或 last_check")
+        return v
+
+    @field_validator("sort_order")
+    @classmethod
+    def validate_sort_order(cls, v):
+        if v.upper() not in ("ASC", "DESC"):
+            raise ValueError("排序方式必须是 ASC 或 DESC")
+        return v.upper()
+
+
+class ProxyDeleteItem(BaseModel):
+    ip: str
+    port: int = Field(ge=1, le=65535)
+
+
+class BatchDeleteRequest(BaseModel):
+    proxies: List[ProxyDeleteItem] = Field(max_length=1000)
+
+
+class PluginToggleRequest(BaseModel):
+    enabled: bool
+
+
+class ExportRequest(BaseModel):
+    format: str = Field(pattern=r"^(csv|txt|json)$")
+    protocol: Optional[str] = None
+    limit: int = Field(default=10000, ge=1, le=100000)