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/Dashboard.tsx

@@ -5,6 +5,7 @@ import { Link } from 'react-router-dom'
 import { PieChart, Pie, Cell, ResponsiveContainer, Tooltip, RadialBarChart, RadialBar, PolarAngleAxis } from 'recharts'
 import { Users, AlertTriangle, CheckSquare, DollarSign, ArrowRight, RefreshCw, FileText, Calendar, TrendingUp, Briefcase, Calculator, Wallet, Building2, Receipt, Check, X, Clock, LayoutDashboard, ListTodo, ShieldAlert, UserPlus, AlertCircle, Download, ChevronRight, TrendingDown, ShieldCheck, Lightbulb, BookOpen, Sparkles, Repeat, XCircle, Loader2 } from 'lucide-react'
 import api from '../lib/api'
+import { dashboardApi, rosterApi } from '../lib/api-services'
 import { useAuthStore } from '../store/authStore'
 import Card from '../components/ui/Card'
 import Button from '../components/ui/Button'
@@ -57,10 +58,7 @@ export default function Dashboard() {
 
   const { data: expiringContracts } = useQuery<any>({
     queryKey: ['expiring-contracts'],
-    queryFn: async () => {
-      const res = await api.get('/roster/contracts/expiring') as any
-      return res.data
-    },
+    queryFn: () => rosterApi.expiringContracts(),
   })
 
   const currentMonth = new Date().toISOString().slice(0, 7)
@@ -75,18 +73,12 @@ export default function Dashboard() {
 
   const { data: complianceScore } = useQuery<any>({
     queryKey: ['compliance-score'],
-    queryFn: async () => {
-      const res = await api.get('/dashboard/compliance-score') as any
-      return res.data
-    },
+    queryFn: () => dashboardApi.healthCheck(),
   })
 
   const { data: workforceStats } = useQuery<any>({
     queryKey: ['workforce-stats'],
-    queryFn: async () => {
-      const res = await api.get('/dashboard/workforce-stats') as any
-      return res.data
-    },
+    queryFn: () => dashboardApi.workforceStats(),
   })
 
   const resolveMutation = useMutation({