Add metrics manifest for dashboard and rule change tracking

[mhotan]

Summary

• Adds metrics-manifest.yaml — an auto-generated list of all metric names from shipped Grafana dashboards and PrometheusRule CRDs
• Adds scripts/extract-metrics.py to extract metrics from dashboard JSON and PrometheusRule templates
• Adds make generate-metrics-manifest target
• Updates CLAUDE.md with instructions for maintaining the metrics glossary

Why

When dashboard panels or PrometheusRules change (metrics added, removed, renamed), the customer-facing metrics glossary in unionai-docs needs to be updated. Today there's no signal in PRs that this is needed.

The manifest makes metric changes visible in PR diffs, so Copilot and reviewers can flag when docs updates are needed.

How it works

1. scripts/extract-metrics.py parses dashboard JSON expr fields and PrometheusRule record:/alert:/expr: blocks
2. Outputs a sorted YAML manifest of all metric names, recording rules, and alert names
3. When a PR modifies dashboards or rules, the contributor runs make generate-metrics-manifest and commits the diff
4. Reviewers (and Copilot) see exactly which metrics changed

Test plan

• make generate-metrics-manifest produces clean output
• Verify manifest covers all metrics in both dashboards and both PrometheusRule files

🤖 Generated with Claude Code

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