docs(lab8): submit Lab 8 — SRE & Monitoring

[linxel]

Goal

Configure Prometheus and Grafana for QuickNotes monitoring with Golden Signals dashboard and alert.

Changes

• Add Prometheus config with scrape job for QuickNotes
• Add Grafana provisioning for datasource and dashboard
• Create Golden Signals dashboard with 4 panels (Traffic, Error Ratio, Notes Count, Health)
• Add alert rule for high error rate (>5% for 5min)
• Add runbook for high error rate alert with triage steps

Testing

• Prometheus scrapes QuickNotes: health=up ✓
• Grafana dashboard shows all 4 panels with data ✓
• Alert rule configured with 5min sustain ✓
• Runbook complete with triage, mitigations, post-incident ✓

Checklist

• Title is a clear sentence (≤ 70 chars)
• Commits are signed
• submissions/lab8.md updated