feat(content): 修复服务并添加chapters/knowledge-points/questions模块

- database.ts 导出db常量替代getDb()函数

- env.ts JWT_SECRET/ES_URL/NEO4J_URL改optional加DEV_MODE

- neo4j.ts driver惰性创建+try/catch+connectionTimeout:3000

- health/lifecycle改用Drizzle原生查询

- textbooks.schema修复integer到int+导出NewTextbook类型

- 新建chapters/knowledge-points/questions三模块CRUD

- knowledge-points含Neo4j前置依赖图非阻塞查询

- content-init.sql创建4张表

端到端验证: textbooks/chapters/knowledge-points/questions全CRUD通过

services/content/src/chapters/chapters.module.ts

@@ -0,0 +1,10 @@
+import { Module } from "@nestjs/common";
+import { ChaptersController } from "./chapters.controller.js";
+import { ChaptersService } from "./chapters.service.js";
+
+@Module({
+  controllers: [ChaptersController],
+  providers: [ChaptersService],
+  exports: [ChaptersService],
+})
+export class ChaptersModule {}