feat: telemetry alert rules with webhook delivery

core.alert_rules (migration 00012) — heartbeat_silence and error_spike
rules evaluated by a 60s backend ticker. Transition-based firing:
alert.fired on breach, alert.resolved on recovery, both first-class
webhook event types riding the signed dispatcher + realtime stream.
Dashboard manages rules on the Integrations page.

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Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

apps/backend/internal/services/webhooks.go

@@ -31,6 +31,8 @@ const (
 	WebhookEventIssueCreated    = "issue.created"
 	WebhookEventDeployMarker    = "deploy.marker"
 	WebhookEventTest            = "webhook.test"
+	WebhookEventAlertFired      = "alert.fired"
+	WebhookEventAlertResolved   = "alert.resolved"
 	WebhookEventDocumentCreated = "document.created"
 	WebhookEventDocumentUpdated = "document.updated"
 	WebhookEventDocumentDeleted = "document.deleted"
@@ -43,6 +45,8 @@ var webhookEventTypes = map[string]bool{
 	WebhookEventIssueCreated:    true,
 	WebhookEventDeployMarker:    true,
 	WebhookEventTest:            true,
+	WebhookEventAlertFired:      true,
+	WebhookEventAlertResolved:   true,
 	WebhookEventJobRun:          true,
 	WebhookEventDocumentCreated: true,
 	WebhookEventDocumentUpdated: true,