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/src/data_ana/config.py

@@ -0,0 +1,18 @@
+"""配置管理."""
+from pydantic_settings import BaseSettings
+
+
+class Settings(BaseSettings):
+    """应用配置."""
+
+    port: int = 3006
+    clickhouse_host: str = "localhost"
+    clickhouse_port: int = 8123
+    clickhouse_database: str = "edu_analytics"
+    otel_endpoint: str = "http://localhost:4318"
+    log_level: str = "info"
+
+    model_config = {"env_file": ".env", "env_prefix": ""}
+
+
+settings = Settings()