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.

backend/src/utils/tokens.ts

@@ -1,7 +1,6 @@
 import jwt from 'jsonwebtoken'
 import crypto from 'crypto'
-
-const JWT_SECRET = process.env['JWT_SECRET'] ?? 'brainwave-dev-secret-change-in-production'
+import { config } from '../config.js'
 
 export interface JwtPayload {
   userId: number
@@ -11,11 +10,11 @@ export interface JwtPayload {
 }
 
 export function signToken(payload: JwtPayload): string {
-  return jwt.sign(payload, JWT_SECRET, { expiresIn: '24h' })
+  return jwt.sign(payload, config.jwtSecret, { expiresIn: '24h' })
 }
 
 export function verifyToken(token: string): JwtPayload {
-  return jwt.verify(token, JWT_SECRET) as JwtPayload
+  return jwt.verify(token, config.jwtSecret) as JwtPayload
 }
 
 export function generateVerificationToken(): string {