feat(content): graphql subgraph with dataloader for textbook/chapter/kp/question

- GraphQLModule: Apollo Federation 2 at /graphql

- Textbook/Chapter/KnowledgePoint/Question @key with @ResolveReference

- RouterAuthGuard: validate Router-Authorization header (ADR-036)

- batchFind methods added to 4 repositories

- Domain modules export repositories for GraphqlModule injection

services/content/src/questions/questions.module.ts

@@ -1,12 +1,13 @@
 import { Module } from "@nestjs/common";
 import { QuestionsController } from "./questions.controller.js";
 import { QuestionsService } from "./questions.service.js";
+import { QuestionsRepository } from "./questions.repository.js";
 import { OutboxModule } from "../shared/outbox/outbox.module.js";
 
 @Module({
   imports: [OutboxModule],
   controllers: [QuestionsController],
-  providers: [QuestionsService],
-  exports: [QuestionsService],
+  providers: [QuestionsService, QuestionsRepository],
+  exports: [QuestionsService, QuestionsRepository],
 })
 export class QuestionsModule {}

services/content/src/questions/questions.repository.ts

@@ -1,4 +1,4 @@
-import { eq, like, or, and, count } from "drizzle-orm";
+import { eq, like, or, and, count, inArray } from "drizzle-orm";
 import { getDb } from "../config/database.js";
 import {
   questions,
@@ -16,6 +16,14 @@ export class QuestionsRepository {
     return result;
   }
 
+  /**
+   * 批量查询（DataLoader @key 解析器使用，ADR-035）
+   */
+  async batchFind(ids: string[]): Promise<Question[]> {
+    if (ids.length === 0) return [];
+    return getDb().select().from(questions).where(inArray(questions.id, ids));
+  }
+
   async findByKnowledgePointId(knowledgePointId: string): Promise<Question[]> {
     return getDb()
       .select()