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/shared/errors/application-error.ts

@@ -0,0 +1,96 @@
+export type ErrorType =
+  | 'validation'
+  | 'not_found'
+  | 'permission_denied'
+  | 'conflict'
+  | 'business'
+  | 'database'
+  | 'internal';
+
+export interface ErrorDetails {
+  [key: string]: unknown;
+}
+
+export abstract class ApplicationError extends Error {
+  abstract readonly type: ErrorType;
+  abstract readonly statusCode: number;
+  readonly code: string;
+  readonly details?: ErrorDetails;
+  // FIX #1: traceId 改为可写，以便 GlobalErrorFilter 注入请求级 traceId
+  traceId?: string;
+
+  constructor(message: string, code: string, details?: ErrorDetails) {
+    super(message);
+    this.name = this.constructor.name;
+    this.code = code;
+    this.details = details;
+  }
+
+  toJSON(): Record<string, unknown> {
+    return {
+      success: false,
+      error: {
+        code: this.code,
+        message: this.message,
+        details: this.details,
+        traceId: this.traceId,
+      },
+    };
+  }
+}
+
+export class ValidationError extends ApplicationError {
+  readonly type = 'validation' as const;
+  readonly statusCode = 400;
+  constructor(message: string, details?: ErrorDetails) {
+    super(message, 'CONTENT_VALIDATION_ERROR', details);
+  }
+}
+
+export class NotFoundError extends ApplicationError {
+  readonly type = 'not_found' as const;
+  readonly statusCode = 404;
+  constructor(resource: string, id: string) {
+    super(`${resource} not found: ${id}`, 'CONTENT_NOT_FOUND', { resource, id });
+  }
+}
+
+export class PermissionDeniedError extends ApplicationError {
+  readonly type = 'permission_denied' as const;
+  readonly statusCode = 403;
+  constructor(permission: string) {
+    super(`Permission denied: ${permission}`, 'CONTENT_PERMISSION_DENIED', { permission });
+  }
+}
+
+export class ConflictError extends ApplicationError {
+  readonly type = 'conflict' as const;
+  readonly statusCode = 409;
+  constructor(message: string, details?: ErrorDetails) {
+    super(message, 'CONTENT_CONFLICT', details);
+  }
+}
+
+export class BusinessError extends ApplicationError {
+  readonly type = 'business' as const;
+  readonly statusCode = 422;
+  constructor(message: string, details?: ErrorDetails) {
+    super(message, 'CONTENT_BUSINESS_ERROR', details);
+  }
+}
+
+export class DatabaseError extends ApplicationError {
+  readonly type = 'database' as const;
+  readonly statusCode = 500;
+  constructor(message: string, details?: ErrorDetails) {
+    super(message, 'CONTENT_DATABASE_ERROR', details);
+  }
+}
+
+export class InternalError extends ApplicationError {
+  readonly type = 'internal' as const;
+  readonly statusCode = 500;
+  constructor(message: string, details?: ErrorDetails) {
+    super(message, 'CONTENT_INTERNAL_ERROR', details);
+  }
+}