feat: implement QuestionBank CRUD with pagination and template query

- Add pagination support to findAll (page, limit query params)
- Add findByTemplateId method to service
- Add GET /by-template/:templateId endpoint to controller
- Service already includes CRUD for QuestionBank and QuestionBankItem

server/src/auth/roles.guard.ts

@@ -0,0 +1,28 @@
+import { Injectable, CanActivate, ExecutionContext } from '@nestjs/common';
+import { Reflector } from '@nestjs/core';
+import { ROLES_KEY } from './roles.decorator';
+import { UserRole } from '../user/user-role.enum';
+
+@Injectable()
+export class RolesGuard implements CanActivate {
+  constructor(private reflector: Reflector) {}
+
+  canActivate(context: ExecutionContext): boolean {
+    const requiredRoles = this.reflector.getAllAndOverride<UserRole[]>(
+      ROLES_KEY,
+      [context.getHandler(), context.getClass()],
+    );
+
+    if (!requiredRoles) {
+      return true;
+    }
+
+    const { user } = context.switchToHttp().getRequest();
+    // User might not be injected yet if auth guard fails, but auth guard runs first usually.
+    if (!user) {
+      return false;
+    }
+
+    return requiredRoles.includes(user.role);
+  }
+}