feat(p4): content analysis service with Neo4j knowledge graph and ClickHouse analytics

P4 阶段交付物：
- services/content: 内容资源服务（NestJS）
  - textbooks: 教材 CRUD + 知识图谱绑定
  - config/neo4j.ts: Neo4j driver 单例
  - textbooks.service.ts: MySQL CRUD + Neo4j 知识图谱（createKnowledgeGraph/getPrerequisites）
  - package.json: 补充 @opentelemetry/sdk-node + exporter-trace-otlp-http
- services/data-ana: 数据分析服务（Python FastAPI）
  - main.py: FastAPI + /healthz + class_performance + student_weakness 骨架
  - clickhouse_client.py: ClickHouse 客户端封装
  - config.py: 环境变量配置
- packages/shared-proto/proto/content.proto: TextbookService + KnowledgeGraphService 契约
- packages/shared-proto/proto/analytics.proto: AnalyticsService 契约（class_performance/student_weakness）

services/content/src/textbooks/textbooks.service.ts

@@ -0,0 +1,69 @@
+import { Injectable } from '@nestjs/common';
+import { getDb } from '../config/database.js';
+import { neo4jDriver } from '../config/neo4j.js';
+import { textbooks, chapters, knowledgePoints } from './textbooks.schema.js';
+import { v4 as uuidv4 } from 'uuid';
+import { eq } from 'drizzle-orm';
+
+@Injectable()
+export class TextbooksService {
+  async create(data: { title: string; subjectId: string; gradeId: string; version: string }) {
+    const id = uuidv4();
+    const db = getDb();
+    await db.insert(textbooks).values({ id, ...data });
+    return { id, ...data };
+  }
+
+  async list() {
+    const db = getDb();
+    return db.select().from(textbooks);
+  }
+
+  async getById(id: string) {
+    const db = getDb();
+    const [result] = await db.select().from(textbooks).where(eq(textbooks.id, id));
+    return result;
+  }
+
+  // 知识图谱：在 Neo4j 中创建知识点节点和关系
+  async createKnowledgeGraph(knowledgePointId: string, title: string, prerequisiteIds: string[]): Promise<void> {
+    const session = neo4jDriver.session();
+    try {
+      await session.executeWrite((tx) =>
+        tx.run(
+          'MERGE (kp:KnowledgePoint {id: $id, title: $title})',
+          { id: knowledgePointId, title }
+        )
+      );
+
+      for (const prereqId of prerequisiteIds) {
+        await session.executeWrite((tx) =>
+          tx.run(
+            `MATCH (prereq:KnowledgePoint {id: $prereqId}), (kp:KnowledgePoint {id: $kpId})
+             MERGE (prereq)-[:PREREQUISITE_OF]->(kp)`,
+            { prereqId, kpId: knowledgePointId }
+          )
+        );
+      }
+    } finally {
+      await session.close();
+    }
+  }
+
+  // 查询知识图谱（前置知识点）
+  async getPrerequisites(knowledgePointId: string): Promise<unknown[]> {
+    const session = neo4jDriver.session();
+    try {
+      const result = await session.executeRead((tx) =>
+        tx.run(
+          `MATCH (kp:KnowledgePoint {id: $id})<-[:PREREQUISITE_OF*1..5]-(prereq)
+           RETURN prereq.id as id, prereq.title as title`,
+          { id: knowledgePointId }
+        )
+      );
+      return result.records.map((r) => ({ id: r.get('id'), title: r.get('title') }));
+    } finally {
+      await session.close();
+    }
+  }
+}