feat(p6): production hardening with circuit breaker, backup, monitoring and chaos engineering

P6 生产硬化阶段交付物（46 文件）：

## 1. API Gateway 中间件链（services/api-gateway/internal/middleware/）
- circuit-breaker.go: gobreaker v2 熔断器（5s 窗口/50% 错误率/30s OPEN→HALF_OPEN）
- ratelimit.go: 令牌桶限流（sync.Map + cleanup goroutine，默认 100rps/20 burst）
- cors.go: CORS 中间件（CORS_ORIGINS 环境变量）
- recovery.go: panic 恢复 + uuid request_id
- security.go: 安全头 + 请求体 10MB 限制
- requestid.go: 请求 ID 注入
- health/health.go: /healthz + /readyz 健康检查
- main.go: 重写注册全部中间件链（Recovery→RequestID→CORS→Security→BodyLimit→RateLimit→CircuitBreaker→Auth）

## 2. 基础设施硬化（infra/）
- backup/backup-mysql.sh: MySQL 全量备份（mysqldump+gzip，按服务独立）
- backup/restore-mysql.sh: 恢复脚本
- backup/backup-cron.sh: cron 调度入口（5 服务批量备份）
- alertmanager/alertmanager.yml: 告警路由（webhook + 邮件示例）
- prometheus/rules.yml: 8 条告警规则（服务可用性/性能/资源 3 组）
- grafana/dashboards/microservices-overview.json: 4 panel 仪表盘
- grafana/provisioning/: 数据源和仪表盘 provisioning
- k8s/namespace.yaml: 4 命名空间（edu-system/services/monitoring/ingress）
- k8s/api-gateway-deployment.yaml: Deployment + Service 骨架
- chaos/experiments.yaml: 3 个 Litmus 混沌实验（pod-kill/network-latency/disk-fill）
- docker-compose.monitoring.yml: 监控栈 profile
- security/secrets.example.env: 8 项密钥占位符
- security/waf-rules.conf: ModSecurity WAF 规则骨架

## 3. 业务服务健康检查 + 优雅停机（5 个 NestJS 服务）
- services/{iam,core-edu,content,msg,classes}/src/shared/health/: /healthz + /readyz
- services/{iam,core-edu,content,msg,classes}/src/shared/lifecycle/: OnModuleInit + OnApplicationShutdown

## 4. Python 服务健康检查
- services/{ai,data-ana}/src/health/health.py: FastAPI APIRouter

## 5. 运维文档
- docs/architecture/runbooks/p6-hardening.md: P6 总览 Runbook（9 章节）
- docs/architecture/runbooks/incident-response.md: 事件响应手册（5 章节）
- docs/architecture/004-p6-addendum.md: 004 架构补记 P6 章节
- docs/troubleshooting/known-issues-p6-addendum.md: 15 条 P6 场景→技术映射

## 验收信号
- RPO ≤ 15min（MySQL 备份 + binlog PITR）
- RTO ≤ 30min（K8s 滚动更新 + DNS 切换）
- P99 ≤ 500ms（熔断 + 限流 + 缓存）
- 熔断器错误率 > 50% 触发 OPEN
- 限流 100rps/20 burst
- 备份保留 7 天
- 混沌实验每月 1 次

infra/docker-compose.monitoring.yml

@@ -0,0 +1,119 @@
+# 监控栈 docker-compose（独立 profile）
+# 使用方式: docker compose -f docker-compose.monitoring.yml --profile monitoring up -d
+version: "3.9"
+
+networks:
+  edu-network:
+    name: edu-network
+    external: true
+
+volumes:
+  prometheus-data:
+    name: edu-prometheus-data
+  alertmanager-data:
+    name: edu-alertmanager-data
+  grafana-data:
+    name: edu-grafana-data
+
+services:
+  # ============================================================
+  # Prometheus - 指标采集与存储
+  # ============================================================
+  prometheus:
+    image: prom/prometheus:v2.54.1
+    container_name: edu-prometheus
+    profiles: ["monitoring"]
+    restart: unless-stopped
+    command:
+      - "--config.file=/etc/prometheus/prometheus.yml"
+      - "--storage.tsdb.path=/prometheus"
+      - "--storage.tsdb.retention.time=15d"
+      - "--web.enable-lifecycle"
+      - "--web.enable-admin-api"
+    ports:
+      - "9090:9090"
+    volumes:
+      - ./prometheus.yml:/etc/prometheus/prometheus.yml:ro
+      - ./prometheus/rules.yml:/etc/prometheus/rules.yml:ro
+      - prometheus-data:/prometheus
+    networks:
+      - edu-network
+
+  # ============================================================
+  # Alertmanager - 告警路由与抑制
+  # ============================================================
+  alertmanager:
+    image: prom/alertmanager:v0.27.0
+    container_name: edu-alertmanager
+    profiles: ["monitoring"]
+    restart: unless-stopped
+    command:
+      - "--config.file=/etc/alertmanager/alertmanager.yml"
+      - "--storage.path=/alertmanager"
+    ports:
+      - "9093:9093"
+    volumes:
+      - ./alertmanager/alertmanager.yml:/etc/alertmanager/alertmanager.yml:ro
+      - alertmanager-data:/alertmanager
+    networks:
+      - edu-network
+    depends_on:
+      - prometheus
+
+  # ============================================================
+  # Grafana - 可视化
+  # ============================================================
+  grafana:
+    image: grafana/grafana:11.2.2
+    container_name: edu-grafana
+    profiles: ["monitoring"]
+    restart: unless-stopped
+    environment:
+      - GF_SECURITY_ADMIN_USER=${GRAFANA_ADMIN_USER:-admin}
+      - GF_SECURITY_ADMIN_PASSWORD=${GRAFANA_ADMIN_PASSWORD:-admin}
+      - GF_USERS_ALLOW_SIGN_UP=false
+      - GF_AUTH_ANONYMOUS_ENABLED=false
+    ports:
+      - "3000:3000"
+    volumes:
+      - ./grafana/provisioning:/etc/grafana/provisioning:ro
+      - ./grafana/dashboards:/var/lib/grafana/dashboards:ro
+      - grafana-data:/var/lib/grafana
+    networks:
+      - edu-network
+    depends_on:
+      - prometheus
+
+  # ============================================================
+  # node-exporter - 主机指标采集
+  # ============================================================
+  node-exporter:
+    image: prom/node-exporter:v1.8.2
+    container_name: edu-node-exporter
+    profiles: ["monitoring"]
+    restart: unless-stopped
+    command:
+      - "--path.rootfs=/host"
+    ports:
+      - "9100:9100"
+    volumes:
+      - /proc:/host/proc:ro
+      - /sys:/host/sys:ro
+      - /:/host:ro
+    networks:
+      - edu-network
+
+  # ============================================================
+  # blackbox-exporter - 黑盒探测（HTTP / TCP / ICMP）
+  # ============================================================
+  blackbox-exporter:
+    image: prom/blackbox-exporter:v0.25.0
+    container_name: edu-blackbox-exporter
+    profiles: ["monitoring"]
+    restart: unless-stopped
+    ports:
+      - "9115:9115"
+    volumes:
+      - ./blackbox/blackbox.yml:/etc/blackbox_exporter/config.yml:ro
+    networks:
+      - edu-network