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/ExamEditor.tsx

@@ -1,7 +1,7 @@
 import { useState, useEffect, useCallback } from 'react'
 import { useParams, useNavigate } from 'react-router-dom'
-import { apiFetch } from '../utils/api'
-import type { Exam, Question, QuestionType, Choice, MatchItem } from '../types'
+import * as examApi from '../api/examApi'
+import type { Exam, Question, QuestionType, Choice } from '../types'
 
 const QUESTION_TYPES: { value: QuestionType; label: string }[] = [
   { value: 'multiple-choice', label: 'Multiple Choice' },
@@ -61,9 +61,9 @@ export default function ExamEditor() {
   useEffect(() => {
     if (isNew) return
     setLoading(true)
-    apiFetch<{ exam: Exam }>(`/api/exams/${examId}`)
+    examApi.getExam(examId!)
       .then((data) => {
-        setExam(data.exam)
+        setExam(data)
         setHasChanges(false)
       })
       .catch((e) => setError((e as Error).message))
@@ -111,18 +111,12 @@ export default function ExamEditor() {
     setError(null)
     try {
       if (isNew) {
-        const data = await apiFetch<{ id: number }>('/api/exams', {
-          method: 'POST',
-          body: JSON.stringify({ exam }),
-        })
+        const data = await examApi.createExam(exam)
         setSaveMsg('Exam created successfully')
         setHasChanges(false)
         navigate(`/exam-editor/${data.id}`, { replace: true })
       } else {
-        await apiFetch(`/api/exams/${examId}`, {
-          method: 'PUT',
-          body: JSON.stringify({ exam }),
-        })
+        await examApi.updateExam(examId!, exam)
         setSaveMsg('Exam saved')
         setHasChanges(false)
       }