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）

packages/shared-proto/proto/analytics.proto

@@ -0,0 +1,61 @@
+syntax = "proto3";
+
+package next_edu_cloud.analytics.v1;
+
+service AnalyticsService {
+  rpc GetClassPerformance(GetClassPerformanceRequest) returns (ClassPerformance);
+  rpc GetStudentWeakness(GetStudentWeaknessRequest) returns (StudentWeakness);
+  rpc GetLearningTrend(GetLearningTrendRequest) returns (LearningTrend);
+}
+
+message GetClassPerformanceRequest {
+  string class_id = 1;
+  string subject_id = 2;
+  int64 start_date = 3;
+  int64 end_date = 4;
+}
+
+message ClassPerformance {
+  string class_id = 1;
+  double average_score = 2;
+  double pass_rate = 3;
+  repeated StudentScore scores = 4;
+}
+
+message StudentScore {
+  string student_id = 1;
+  double score = 2;
+  string grade = 3;
+}
+
+message GetStudentWeaknessRequest {
+  string student_id = 1;
+  string subject_id = 2;
+}
+
+message StudentWeakness {
+  string student_id = 1;
+  repeated WeakPoint weak_points = 2;
+}
+
+message WeakPoint {
+  string knowledge_point_id = 1;
+  string title = 2;
+  double mastery = 3;
+}
+
+message GetLearningTrendRequest {
+  string student_id = 1;
+  int64 start_date = 2;
+  int64 end_date = 3;
+}
+
+message LearningTrend {
+  string student_id = 1;
+  repeated TrendPoint points = 2;
+}
+
+message TrendPoint {
+  int64 date = 1;
+  double score = 2;
+}

packages/shared-proto/proto/content.proto

@@ -0,0 +1,47 @@
+syntax = "proto3";
+
+package next_edu_cloud.content.v1;
+
+service TextbookService {
+  rpc CreateTextbook(CreateTextbookRequest) returns (Textbook);
+  rpc GetTextbook(GetTextbookRequest) returns (Textbook);
+  rpc ListTextbooks(ListTextbooksRequest) returns (ListTextbooksResponse);
+}
+
+service KnowledgeGraphService {
+  rpc GetPrerequisites(GetPrerequisitesRequest) returns (KnowledgePointsResponse);
+  rpc GetLearningPath(GetLearningPathRequest) returns (LearningPath);
+}
+
+message Textbook {
+  string id = 1;
+  string title = 2;
+  string subject_id = 3;
+  string grade_id = 4;
+  string version = 5;
+}
+
+message CreateTextbookRequest {
+  string title = 1;
+  string subject_id = 2;
+  string grade_id = 3;
+  string version = 4;
+}
+
+message GetTextbookRequest { string id = 1; }
+message ListTextbooksRequest { string subject_id = 1; string grade_id = 2; }
+message ListTextbooksResponse { repeated Textbook textbooks = 1; }
+
+message KnowledgePoint {
+  string id = 1;
+  string title = 2;
+}
+
+message GetPrerequisitesRequest { string knowledge_point_id = 1; }
+message KnowledgePointsResponse { repeated KnowledgePoint points = 1; }
+
+message GetLearningPathRequest { string student_id = 1; string subject_id = 2; }
+message LearningPath {
+  repeated KnowledgePoint points = 1;
+  repeated string recommended_order = 2;
+}