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/middleware/validate.ts

@@ -0,0 +1,43 @@
+import { z } from 'zod'
+import type { Request, Response, NextFunction } from 'express'
+
+function getFirstIssueMessage(error: z.ZodError): string {
+  const issue = error.issues[0]
+  return issue?.message ?? 'Validation failed'
+}
+
+export function validateBody<T extends z.ZodTypeAny>(schema: T) {
+  return (req: Request, res: Response, next: NextFunction): void => {
+    const result = schema.safeParse(req.body)
+    if (!result.success) {
+      res.status(400).json({ error: getFirstIssueMessage(result.error) })
+      return
+    }
+    req.body = result.data as z.infer<T>
+    next()
+  }
+}
+
+export function validateQuery<T extends z.ZodTypeAny>(schema: T) {
+  return (req: Request, res: Response, next: NextFunction): void => {
+    const result = schema.safeParse(req.query)
+    if (!result.success) {
+      res.status(400).json({ error: getFirstIssueMessage(result.error) })
+      return
+    }
+    ;(req as unknown as Record<string, unknown>).parsedQuery = result.data
+    next()
+  }
+}
+
+export function validateParams<T extends z.ZodTypeAny>(schema: T) {
+  return (req: Request, res: Response, next: NextFunction): void => {
+    const result = schema.safeParse(req.params)
+    if (!result.success) {
+      res.status(400).json({ error: getFirstIssueMessage(result.error) })
+      return
+    }
+    Object.assign(req.params, result.data)
+    next()
+  }
+}