fix: 题库创建唯一约束检查 + 前端错误消息透传

server/src/assessment/services/question-bank.service.ts

@@ -90,6 +90,12 @@ export class QuestionBankService {
     if (!createDto.name || !createDto.name.trim()) {
       throw new BadRequestException('Question bank name is required');
     }
+    if (createDto.templateId) {
+      const existing = await this.bankRepository.findOne({ where: { templateId: createDto.templateId } });
+      if (existing) {
+        throw new BadRequestException('该模板已关联题库，一个模板只能创建一个题库');
+      }
+    }
     const bankData: any = {
       name: createDto.name,
       description: createDto.description || '',
@@ -98,7 +104,7 @@ export class QuestionBankService {
       status: QuestionBankStatus.DRAFT,
     };
     if (createDto.templateId) {
-      bankData.template = { id: createDto.templateId };
+      bankData.templateId = createDto.templateId;
     }
     const bank = this.bankRepository.create(bankData as any);
     return this.bankRepository.save(bank as unknown as QuestionBank);