Completes metric-threshold alerting end-to-end: /metric-alert-rules
list/new/edit routes (mirroring log-scan-rules) with metric/comparator/
threshold fields, the workload scope picker, ToggleSwitch, and a
ConfirmDialog delete flow; an api.ts MetricAlertRule CRUD client; an
"Observe" nav entry; and a full metricalert.* i18n namespace (en/ru
parity). Create-form cooldown defaults to 300s to match the server.
Rules are now manageable in the WebUI; breaches already surface in the
per-app activity timeline and fire any configured event-trigger webhook.
Reviewed: typescript APPROVE (0 CRITICAL/HIGH).
alexei.dolgolyov
7576f54e76