refactor: 全量迁移前端 API 调用到统一 api-services 服务层

- 新建 api-services-raw.ts 导出原始 axios 方法供特殊端点使用
- 完成 api-services.ts 全领域覆盖（auth/employee/roster/dashboard/attendance/payroll/socialInsurance/commercialInsurance/termination/policies/evidence/audit/calendar/companyFiles/notifications/settings/ai/platform/portal/survey/search）
- 迁移所有 47+ 页面文件：pages/、pages/roster/、pages/portal/、pages/platform/、pages/auth/、pages/dashboard/、pages/compliance/
- 移除所有直接 import api from '../../lib/api' 引用
- 修复 Termination.tsx / WorkProcess.tsx 中 string|null 类型错误
- 修复 SocialInsurance.tsx 中 api-services-raw delete 导入名
- 修复 PlatformLogin.tsx 变量遮蔽问题
- tsc --noEmit 零错误，vite build 成功

frontend/src/components/HelpModal.tsx

@@ -3,7 +3,7 @@ import { HelpCircle, Search, ChevronDown, ChevronRight, Sparkles,
   Home, Users, FileText, Calculator, Shield, UserX, Bot, 
   Bell, Settings, Lightbulb, AlertTriangle, CheckCircle, Phone } from 'lucide-react'
 import Modal from './ui/Modal'
-import api from '../lib/api'
+import { aiApi } from '../lib/api-services'
 import clsx from 'clsx'
 
 interface HelpCategory {
@@ -267,8 +267,8 @@ export default function HelpModal({ open, onClose }: { open: boolean; onClose: (
       setRagLoading(true)
       setRagError(false)
       try {
-        const res = await api.post('/ai/rag/help-search', { query: searchQuery, topK: 8 }) as any
-        setRagResults(res.data?.results || [])
+        const res = await aiApi.ragHelpSearch(searchQuery, 8) as any
+        setRagResults(res?.results || [])
       } catch {
         setRagError(true)
         setRagResults([])