Adds alerting stanza to application.yml with all AlertingProperties fields backed by env-var overrides. Creates docs/alerting.md covering six condition kinds (with example JSON), template variables, webhook setup (Slack/PagerDuty examples), silence patterns, circuit-breaker and retention troubleshooting, and Prometheus metrics reference. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>