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/ai/ai.module.ts

@@ -0,0 +1,8 @@
+import { Module } from '@nestjs/common';
+import { EmbeddingService } from './embedding.service';
+
+@Module({
+  providers: [EmbeddingService],
+  exports: [EmbeddingService],
+})
+export class AiModule {}