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/main.py

@@ -0,0 +1,75 @@
+"""数据分析服务入口."""
+from contextlib import asynccontextmanager
+from fastapi import FastAPI
+from opentelemetry import trace
+from opentelemetry.sdk.trace import TracerProvider
+from opentelemetry.sdk.trace.export import BatchSpanProcessor
+from opentelemetry.exporter.otlp.proto.http.trace_exporter import OTLPSpanExporter
+from prometheus_client import make_asgi_app
+import structlog
+
+logger = structlog.get_logger()
+tracer = trace.get_tracer(__name__)
+
+
+def init_tracer() -> None:
+    """初始化 OpenTelemetry."""
+    provider = TracerProvider()
+    exporter = OTLPSpanExporter(endpoint="http://localhost:4318/v1/traces")
+    provider.add_span_processor(BatchSpanProcessor(exporter))
+    trace.set_tracer_provider(provider)
+
+
+@asynccontextmanager
+async def lifespan(app: FastAPI):
+    """应用生命周期."""
+    init_tracer()
+    logger.info("data-ana service starting")
+    yield
+    logger.info("data-ana service stopping")
+
+
+app = FastAPI(
+    title="Data Analytics Service",
+    version="0.1.0",
+    lifespan=lifespan,
+)
+
+# Prometheus 指标
+app.mount("/metrics", make_asgi_app())
+
+
+@app.get("/healthz")
+async def healthz():
+    """健康检查."""
+    return {"status": "ok", "service": "data-ana"}
+
+
+@app.get("/analytics/class/{class_id}/performance")
+async def class_performance(class_id: str):
+    """班级成绩分析."""
+    with tracer.start_as_current_span("class_performance"):
+        # P4 骨架：从 ClickHouse 查询分析数据
+        return {
+            "success": True,
+            "data": {
+                "classId": class_id,
+                "averageScore": 0,
+                "passRate": 0,
+                "message": "P4 skeleton - ClickHouse integration pending",
+            },
+        }
+
+
+@app.get("/analytics/student/{student_id}/weakness")
+async def student_weakness(student_id: str):
+    """学生薄弱知识点分析."""
+    with tracer.start_as_current_span("student_weakness"):
+        return {
+            "success": True,
+            "data": {
+                "studentId": student_id,
+                "weakPoints": [],
+                "message": "P4 skeleton - weakness analysis pending",
+            },
+        }