refactor(frontend): services/api 迁至 src/api，http 迁至 utils/request

对齐 Vue 后台惯例：
- src/api/          域 API（原 services/api）
- src/utils/request.ts  HTTP 封装（原 services/http.ts）
- src/utils/export.ts  客户端导出工具
- src/utils/index.ts   工具统一出口

全局导入改为 @/api 与 @/utils/request，tsc + build 通过。

frontend/src/api/system/approval.ts

@@ -0,0 +1,28 @@
+// 审批流程 API // Logan.Li
+
+import { http } from '@/utils/request';
+
+export const approvalWorkflowApi = {
+  list: async (params?: { category?: string }) => http.get('/approval-workflows', params),
+  get: async (id: number | string) => http.get(`/approval-workflows/${id}`),
+  create: async (data: Record<string, unknown>) => http.post('/approval-workflows', data),
+  update: async (id: number | string, data: Record<string, unknown>) => http.put(`/approval-workflows/${id}`, data),
+  delete: async (id: number | string) => http.delete(`/approval-workflows/${id}`),
+  setDefault: async (id: number | string) => http.put(`/approval-workflows/${id}/default`),
+  getSteps: async (id: number | string) => http.get(`/approval-workflows/${id}/steps`),
+};
+
+export const approvalApi = {
+  getTemplates: async (params?: { type?: string; category?: string }) => http.get('/approvals/templates', params),
+  getTemplate: async (id: number | string) => http.get(`/approvals/templates/${id}`),
+  createTemplate: async (data: Record<string, unknown>) => http.post('/approvals/templates', data),
+  updateTemplate: async (id: number | string, data: Record<string, unknown>) => http.put(`/approvals/templates/${id}`, data),
+  deleteTemplate: async (id: number | string) => http.delete(`/approvals/templates/${id}`),
+  getProcesses: async (params?: { page?: number; page_size?: number; status?: string; category?: string }) =>
+    http.get('/approvals/processes', params),
+  createProcess: async (data: Record<string, unknown>) => http.post('/approvals/processes', data),
+  approveProcess: async (id: number | string, comment?: string) =>
+    http.post(`/approvals/processes/${id}/approve`, { comment }),
+  rejectProcess: async (id: number | string, comment?: string) =>
+    http.post(`/approvals/processes/${id}/reject`, { comment }),
+};