feat(infra): p6 hardening - metrics collection and registry mirror

- 4 services add collectDefaultMetrics for process metrics
- docker-compose.yml images prefixed with docker.m.daocloud.io
- Prometheus v0.51.0 (nonexistent) fixed to v2.51.0
- Grafana port remapped 3000 to 3030 to avoid teacher-portal conflict
- ClickHouse edu_analytics database initialized
- known-issues.md documents 7 new P6 scenario-to-rule mappings

services/content/src/shared/observability/metrics.ts

@@ -1,24 +1,28 @@
-import promClient from 'prom-client';
+import promClient from "prom-client";
 
 const registry = new promClient.Registry();
 // 修复：在本地 registry 上设置默认标签（原代码误用全局 register）
-registry.setDefaultLabels({ service: 'content' });
+registry.setDefaultLabels({ service: "content" });
 
 registry.registerMetric(
   new promClient.Counter({
-    name: 'content_requests_total',
-    help: 'Total number of content requests',
-    labelNames: ['method', 'endpoint', 'status'],
+    name: "content_requests_total",
+    help: "Total number of content requests",
+    labelNames: ["method", "endpoint", "status"],
   }),
 );
 
 registry.registerMetric(
   new promClient.Histogram({
-    name: 'content_request_duration_seconds',
-    help: 'Content request duration in seconds',
-    labelNames: ['method', 'endpoint'],
+    name: "content_request_duration_seconds",
+    help: "Content request duration in seconds",
+    labelNames: ["method", "endpoint"],
     buckets: [0.01, 0.05, 0.1, 0.3, 0.5, 1, 3, 5],
   }),
 );
 
+// 自动收集 Node.js 进程级指标（CPU/内存/事件循环/GC等）
+// 这些指标无需业务代码埋点，prom-client 自动采集
+promClient.collectDefaultMetrics({ register: registry });
+
 export { registry as metricsRegistry };