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/migrations/add-language-to-user-settings.sql

@@ -0,0 +1,3 @@
+-- Add language column to user_settings table
+ALTER TABLE user_settings
+    ADD COLUMN language TEXT DEFAULT 'zh';