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/database/db/models.go

@@ -140,6 +140,18 @@ func (ns NullCoreProjectRole) Value() (driver.Value, error) {
 	return string(ns.CoreProjectRole), nil
 }
 
+type CoreAlertRule struct {
+	ID        uuid.UUID          `json:"id"`
+	ProjectID uuid.UUID          `json:"project_id"`
+	Name      string             `json:"name"`
+	Kind      string             `json:"kind"`
+	Config    []byte             `json:"config"`
+	Enabled   bool               `json:"enabled"`
+	State     []byte             `json:"state"`
+	CreatedAt pgtype.Timestamptz `json:"created_at"`
+	UpdatedAt pgtype.Timestamptz `json:"updated_at"`
+}
+
 type CoreApiKey struct {
 	ID              uuid.UUID          `json:"id"`
 	ProjectID       uuid.UUID          `json:"project_id"`