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/MyExams.tsx

@@ -1,7 +1,6 @@
 import { useState, useEffect, useCallback } from 'react'
 import { useNavigate } from 'react-router-dom'
-import { apiFetch } from '../utils/api'
-import type { Exam } from '../types'
+import * as examApi from '../api/examApi'
 
 interface SavedExam {
   id: number
@@ -23,7 +22,7 @@ export default function MyExams() {
     setLoading(true)
     setError(null)
     try {
-      const data = await apiFetch<SavedExam[]>('/api/exams')
+      const data = await examApi.listExams()
       setExams(data)
     } catch (e) {
       setError((e as Error).message)
@@ -38,7 +37,7 @@ export default function MyExams() {
 
   const deleteExam = async (id: number) => {
     try {
-      await apiFetch(`/api/exams/${id}`, { method: 'DELETE' })
+      await examApi.deleteExam(id)
       setDeleteConfirm(null)
       void loadExams()
     } catch (e) {