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/platform_service.go

@@ -38,6 +38,7 @@ type PlatformService struct {
 	enc            *secrets.Encryptor
 	dispatcher     *WebhookDispatcher
 	scheduler      *JobScheduler
+	alerts         *alertEvaluator
 }
 
 type BootstrapInput struct {
@@ -230,6 +231,8 @@ func NewPlatformService(repo *repositories.CoreRepository, store *storage.LocalS
 		s.dispatcher.Start(context.Background())
 		s.scheduler = NewJobScheduler(repo.Queries(), enc, logger, s.publishEvent)
 		s.scheduler.Start(context.Background())
+		s.alerts = newAlertEvaluator(repo.Queries(), s.publishEvent, logger)
+		s.alerts.Start(context.Background())
 	}
 	return s
 }
@@ -242,6 +245,9 @@ func (s *PlatformService) Close() {
 	if s.scheduler != nil {
 		s.scheduler.Stop()
 	}
+	if s.alerts != nil {
+		s.alerts.Stop()
+	}
 }
 
 // publishEvent fans a domain event out to realtime SSE subscribers and to