refactor: API口径统一 — 统计函数/员工列表/前端服务层

后端:
- /dashboard/compliance-score 改用 getHealthCheck，与体检诊断同口径
- 新增 /employees/list 端点（不分页，供各页面下拉选择）
- /employees/all-lite 增加 position 字段和 status 筛选参数
- getHealthCheck 未签合同改为查无合同记录的员工（非UNSIGNED类型）

前端:
- 新建 lib/api-services.ts 统一 API 服务层
- employeeApi/rosterApi/dashboardApi/attendanceApi 统一封装
- 6个页面迁移到统一 API 调用:
  - Attendance: employeeApi.list + rosterApi.departments
  - Termination: rosterApi.list + rosterApi.departments
  - Money: rosterApi.list + rosterApi.departments
  - PortalQRModal: employeeApi.list
  - AIAssistant: 3处 employeeApi.list 替代 /roster?pageSize=999
  - Contracts: rosterApi.departments
  - Dashboard: rosterApi.expiringContracts + dashboardApi.healthCheck/workforceStats

frontend/src/pages/Contracts.tsx

@@ -3,6 +3,7 @@ import { useQuery, useMutation, useQueryClient } from '@tanstack/react-query'
 import { Plus, Search, Paperclip, Trash2, X, FileText, Download, Eye } from 'lucide-react'
 import { toast } from 'sonner'
 import api from '../lib/api'
+import { rosterApi } from '../lib/api-services'
 import Card from '../components/ui/Card'
 import Button from '../components/ui/Button'
 import { Input, Label, Select } from '../components/ui/Input'
@@ -66,10 +67,7 @@ export default function Contracts() {
 
   const { data: departmentList } = useQuery<string[]>({
     queryKey: ['roster-departments'],
-    queryFn: async () => {
-      const res = await api.get('/roster/departments') as any
-      return res.data || []
-    },
+    queryFn: () => rosterApi.departments(),
   })
 
   return (