alert-mgmt-07: GET /rules endpoint

[sradco]

Alert Management API — Part 7/14: GET /rules + ListRules

Summary

• GET /api/v1/alerting/rules handler with label, state, matcher, and source filtering
• Management-layer GetRules: merges Prometheus rule groups with relabeled rules, applying label overrides from AlertRelabelConfigs
• Relabeled rule matching with PromQL expression canonicalization and duration comparison
• ListRules: retrieves all relabeled rules with optional PrometheusRule and AlertRule filtering
• New query types: PrometheusRuleOptions, AlertRuleOptions for flexible rule listing
• Extended PrometheusRule type with alert-level state/active alert tracking
• Unit tests for rule merging, relabeled matching, PromQL normalization, and handler behavior

Dependencies

This PR is part of a stacked series. Please review in order.

1. alert-mgmt-01: k8s foundation + health stub skeleton
2. Pending — alert listing, query & filter primitives
3. Pending — relabel config, alerting health & AlertingRule CRD
4. Pending — management foundation
5. Pending — GET /health endpoint + router + server wiring
6. Pending — GET /alerts endpoint
7. → This PR — GET /rules + ListRules
   8–14. Pending — create, delete, classification, platform update, bulk update, docs/CI/e2e, single-rule API