feat: 完善前后端核心功能模块

后端:
- 新增认证(auth)、任务(tasks)、映射(mappings)、对账(reconciliation)、异常(exceptions)、导出(exports) API
- 新增核心模块: database, security, permissions, tenant, exceptions, error_handlers
- 新增数据模型: user, company, reconciliation_task, field_mapping, uploaded_file 等
- 新增服务层: ai_recognizer, file_parser, file_storage, mapping, reconciliation 等
- 添加数据库迁移脚本

前端:
- 新增登录页面和仪表盘页面
- 新增任务列表、任务详情、字段映射页面
- 新增异常处理页面和规则设置页面
- 新增 API 代理路由 /api/[...path]
- 新增 UI 组件库 (button, card, dialog, input, table 等)
- 新增 auth 组件 (ProtectedRoute, PermissionGate)
- 新增 layout 组件 (Header, Sidebar)
- 新增 mapping 组件 (FieldMappingTable, AISuggestionPanel)
- 新增 API 客户端和 hooks (useAsync, useToast, usePermission 等)
- 新增状态管理 (auth-store, company-store, ui-store)
- 集成 Tailwind CSS 和 shadcn/ui 组件库

其他:
- 添加 Alembic 数据库迁移配置
- 添加初始化示例数据脚本
- 更新项目文档

frontend/lib/api/client.ts

@@ -0,0 +1,122 @@
+import axios, { AxiosError, AxiosInstance, AxiosRequestConfig, AxiosResponse } from 'axios';
+
+import type { ApiError, ApiResponse } from './types';
+
+// 创建 Axios 实例
+const createApiClient = (): AxiosInstance => {
+  const baseURL = process.env.NEXT_PUBLIC_API_URL || '';
+
+  const instance = axios.create({
+    baseURL,
+    timeout: 30000,
+    headers: {
+      'Content-Type': 'application/json',
+    },
+  });
+
+  // 请求拦截器
+  instance.interceptors.request.use(
+    (config) => {
+      // 自动添加 JWT Token
+      if (typeof window !== 'undefined') {
+        const token = localStorage.getItem('auth_token');
+        if (token && config.headers) {
+          config.headers.Authorization = `Bearer ${token}`;
+        }
+
+        // 添加企业 ID
+        const companyId = localStorage.getItem('company_id');
+        if (companyId && config.headers) {
+          config.headers['X-Company-ID'] = companyId;
+        }
+      }
+
+      return config;
+    },
+    (error) => {
+      return Promise.reject(error);
+    }
+  );
+
+  // 响应拦截器
+  instance.interceptors.response.use(
+    (response: AxiosResponse) => {
+      return response;
+    },
+    (error: AxiosError<ApiError>) => {
+      // 统一错误处理
+      const apiError: ApiError = {
+        code: 'UNKNOWN_ERROR',
+        message: '未知错误',
+      };
+
+      if (error.response) {
+        // 服务器返回错误
+        const { data, status } = error.response;
+
+        if (data && typeof data === 'object' && 'error' in data) {
+          const errorData = data as { error: { code: string; message: string; details?: unknown } };
+          apiError.code = errorData.error.code;
+          apiError.message = errorData.error.message;
+          apiError.details = errorData.error.details;
+        } else {
+          apiError.code = `HTTP_${status}`;
+          apiError.message = error.message;
+        }
+
+        // 401 未授权 - 跳转登录
+        if (status === 401) {
+          if (typeof window !== 'undefined') {
+            localStorage.removeItem('auth_token');
+            localStorage.removeItem('company_id');
+            window.location.href = '/login';
+          }
+        }
+      } else if (error.request) {
+        // 请求发送但无响应
+        apiError.code = 'NETWORK_ERROR';
+        apiError.message = '网络错误，请检查连接';
+      } else {
+        // 其他错误
+        apiError.message = error.message;
+      }
+
+      return Promise.reject(apiError);
+    }
+  );
+
+  return instance;
+};
+
+// API 客户端单例
+export const apiClient = createApiClient();
+
+// 通用请求方法封装
+export const api = {
+  get: async <T>(url: string, config?: AxiosRequestConfig): Promise<ApiResponse<T>> => {
+    const response = await apiClient.get<T>(url, config);
+    return { data: response.data, status: response.status };
+  },
+
+  post: async <T>(url: string, data?: unknown, config?: AxiosRequestConfig): Promise<ApiResponse<T>> => {
+    const response = await apiClient.post<T>(url, data, config);
+    return { data: response.data, status: response.status };
+  },
+
+  put: async <T>(url: string, data?: unknown, config?: AxiosRequestConfig): Promise<ApiResponse<T>> => {
+    const response = await apiClient.put<T>(url, data, config);
+    return { data: response.data, status: response.status };
+  },
+
+  patch: async <T>(url: string, data?: unknown, config?: AxiosRequestConfig): Promise<ApiResponse<T>> => {
+    const response = await apiClient.patch<T>(url, data, config);
+    return { data: response.data, status: response.status };
+  },
+
+  delete: async <T>(url: string, config?: AxiosRequestConfig): Promise<ApiResponse<T>> => {
+    const response = await apiClient.delete<T>(url, config);
+    return { data: response.data, status: response.status };
+  },
+};
+
+export default apiClient;