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/api/examApi.ts

@@ -0,0 +1,31 @@
+import { apiFetch } from '../utils/api.js'
+import type { Exam } from '../types'
+
+export interface ExamListItem {
+  id: number
+  title: string
+  subtitle: string | null
+  created_at: number
+  updated_at: number
+  question_count: number
+}
+
+export function listExams(): Promise<ExamListItem[]> {
+  return apiFetch('/api/exams')
+}
+
+export function getExam(id: number): Promise<Exam> {
+  return apiFetch(`/api/exams/${id}`)
+}
+
+export function createExam(exam: Exam): Promise<{ id: number; title: string }> {
+  return apiFetch('/api/exams', { method: 'POST', body: JSON.stringify({ exam }) })
+}
+
+export function updateExam(id: number, exam: Exam): Promise<{ success: boolean }> {
+  return apiFetch(`/api/exams/${id}`, { method: 'PUT', body: JSON.stringify({ exam }) })
+}
+
+export function deleteExam(id: number): Promise<{ success: boolean }> {
+  return apiFetch(`/api/exams/${id}`, { method: 'DELETE' })
+}