docs(phase-7): finalize documentation and Bruno collection

[chitrank2050]

Description

Document Phase 7 observability architecture and operational runbooks.

Affected Sections

• Architecture doc: phase-7-observability.md
• Phase log: phases/phase-7.md
• Operational runbook: docs/operations/runbook.md
• mkdocs.yml nav

Content Ideas

• Monitoring architecture diagram (app → Prometheus → Grafana)
• Tracing architecture diagram (app → OTLP collector → Jaeger)
• Dashboard screenshots
• Alert escalation matrix
• Incident response playbook template
• Load test results summary

Additional context

The operational runbook is the "what to do when X breaks" guide. Every alert should link to a runbook section.