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

tests/unit/test_models.py

@@ -0,0 +1,136 @@
+"""模型单元测试"""
+import pytest
+from datetime import datetime
+from app.models.domain import ProxyRaw, Proxy, PluginInfo
+from app.models.schemas import (
+    ProxyCreate,
+    ProxyListRequest,
+    SettingsSchema,
+    BatchDeleteRequest,
+)
+
+
+class TestProxyRaw:
+    """测试 ProxyRaw 领域模型"""
+
+    def test_create_proxy_raw(self):
+        """测试创建原始代理"""
+        proxy = ProxyRaw("192.168.1.1", 8080, "http")
+        assert proxy.ip == "192.168.1.1"
+        assert proxy.port == 8080
+        assert proxy.protocol == "http"
+
+    def test_protocol_normalization(self):
+        """测试协议标准化"""
+        proxy = ProxyRaw("192.168.1.1", 8080, "HTTP")
+        assert proxy.protocol == "http"
+
+    def test_invalid_protocol_defaults_to_http(self):
+        """测试无效协议默认为 http"""
+        proxy = ProxyRaw("192.168.1.1", 8080, "invalid")
+        assert proxy.protocol == "http"
+
+
+class TestProxy:
+    """测试 Proxy 领域模型"""
+
+    def test_create_proxy(self):
+        """测试创建代理实体"""
+        proxy = Proxy(
+            ip="192.168.1.1",
+            port=8080,
+            protocol="http",
+            score=50,
+            response_time_ms=100.5,
+            last_check=datetime.now(),
+            created_at=datetime.now(),
+        )
+        assert proxy.ip == "192.168.1.1"
+        assert proxy.score == 50
+
+
+class TestPluginInfo:
+    """测试 PluginInfo 领域模型"""
+
+    def test_create_plugin_info(self):
+        """测试创建插件信息"""
+        plugin = PluginInfo(
+            id="test_plugin",
+            name="test_plugin",
+            display_name="测试插件",
+            description="用于测试",
+            enabled=True,
+            success_count=10,
+            failure_count=2,
+        )
+        assert plugin.id == "test_plugin"
+        assert plugin.enabled is True
+        assert plugin.success_count == 10
+
+
+class TestProxyCreateSchema:
+    """测试 ProxyCreate Pydantic 模型"""
+
+    def test_valid_proxy_create(self):
+        """测试有效的代理创建"""
+        proxy = ProxyCreate(ip="192.168.1.1", port=8080, protocol="http")
+        assert proxy.ip == "192.168.1.1"
+        assert proxy.port == 8080
+
+    def test_port_validation(self):
+        """测试端口验证"""
+        with pytest.raises(Exception):
+            ProxyCreate(ip="192.168.1.1", port=70000)  # 超出范围
+
+    def test_protocol_validation(self):
+        """测试协议验证"""
+        with pytest.raises(Exception):
+            ProxyCreate(ip="192.168.1.1", port=8080, protocol="invalid")
+
+
+class TestProxyListRequest:
+    """测试 ProxyListRequest 模式"""
+
+    def test_default_values(self):
+        """测试默认值"""
+        request = ProxyListRequest()
+        assert request.page == 1
+        assert request.page_size == 20
+        assert request.sort_by == "last_check"
+        assert request.sort_order == "DESC"
+
+    def test_custom_values(self):
+        """测试自定义值"""
+        request = ProxyListRequest(page=2, page_size=50, protocol="https")
+        assert request.page == 2
+        assert request.page_size == 50
+        assert request.protocol == "https"
+
+
+class TestSettingsSchema:
+    """测试 SettingsSchema"""
+
+    def test_default_settings(self):
+        """测试默认设置"""
+        settings = SettingsSchema()
+        assert settings.crawl_timeout == 30
+        assert settings.validation_timeout == 10
+        assert settings.auto_validate is True
+
+    def test_custom_settings(self):
+        """测试自定义设置"""
+        settings = SettingsSchema(crawl_timeout=60, auto_validate=False)
+        assert settings.crawl_timeout == 60
+        assert settings.auto_validate is False
+
+
+class TestBatchDeleteRequest:
+    """测试 BatchDeleteRequest"""
+
+    def test_valid_batch_delete(self):
+        """测试有效的批量删除"""
+        request = BatchDeleteRequest(proxies=[
+            {"ip": "192.168.1.1", "port": 8080},
+            {"ip": "192.168.1.2", "port": 8081},
+        ])
+        assert len(request.proxies) == 2