feat: Implement API modules for admin, auth, exam, result, and setup functionalities

- Created adminApi.ts for admin-related operations including user management and site settings.
- Developed authApi.ts for authentication processes such as registration, login, and profile management.
- Added examApi.ts for handling exam CRUD operations.
- Introduced resultApi.ts for managing results submission and retrieval.
- Established setupApi.ts for initial setup processes and status checks.
- Created ErrorBoundary component to handle rendering errors gracefully in the frontend.
- Re-exported shared API utilities in index.ts for easier access.

frontend/src/components/Workspace.tsx

@@ -1,7 +1,8 @@
 import { useState, useEffect, useCallback } from 'react'
 import { useNavigate, useParams, Navigate } from 'react-router-dom'
 import { useAuth } from '../contexts/AuthContext'
-import { apiFetch } from '../utils/api'
+import * as examApi from '../api/examApi'
+import * as resultApi from '../api/resultApi'
 import MyExams from './MyExams'
 import MyResults from './MyResults'
 import Settings from './Settings'
@@ -24,9 +25,9 @@ export default function Workspace() {
 
   const loadCounts = useCallback(async () => {
     try {
-      const exams = await apiFetch<{ id: number }[]>('/api/exams')
+      const exams = await examApi.listExams()
       setExamCount(exams.length)
-      const results = await apiFetch<{ results: unknown[]; total: number }>('/api/results')
+      const results = await resultApi.listResults()
       setResultCount(results.total)
     } catch {
       // silently ignore