alert-mgmt-10: classification system

[sradco]

Alert Management API — Part 10/14: classification system

Summary

• Alert rule classification: component and layer assignment via ConfigMap-based override keys
• UpdateAlertRuleClassification and BulkUpdateAlertRuleClassification management methods
• Alert component matcher engine (pkg/alertcomponent): label-based matching with string and regex value matchers for automatic component/layer derivation
• Classification validation (pkg/classification): layer, component, and PromQL label name validation
• AlertRuleClassificationPatch router type with explicit Set flags for distinguishing null vs absent fields
• ConfigMap-based classification override storage (alert_classification_configmap.go)
• Override namespace resolution for classification data persistence
• Extended GetAlerts to enrich alerts with classification data (component, layer, componentFrom, layerFrom)
• Classification design documentation (docs/alert-rule-classification.md)
• Unit tests for classification update, patch parsing, and alert enrichment

Dependencies

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

1. alert-mgmt-01: k8s foundation + health stub skeleton
   2–9. Pending — alert queries, relabel/health, management foundation, endpoints, create, delete
2. → This PR — classification system
   11–14. Pending — platform update, bulk update, docs/CI/e2e, single-rule API