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/textbooks/textbooks.module.ts

@@ -1,9 +1,10 @@
-import { Module } from '@nestjs/common';
-import { TextbooksController } from './textbooks.controller.js';
-import { TextbooksService } from './textbooks.service.js';
+import { Module } from "@nestjs/common";
+import { TextbooksController } from "./textbooks.controller.js";
+import { TextbooksService } from "./textbooks.service.js";
 
 @Module({
   controllers: [TextbooksController],
   providers: [TextbooksService],
+  exports: [TextbooksService],
 })
 export class TextbooksModule {}