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/data-ana/Dockerfile

@@ -0,0 +1,8 @@
+FROM python:3.12-slim
+WORKDIR /app
+RUN pip install uv
+COPY pyproject.toml .
+RUN uv sync --no-dev
+COPY src ./src
+EXPOSE 3006
+CMD ["uv", "run", "uvicorn", "src.data_ana.main:app", "--host", "0.0.0.0", "--port", "3006"]