R-585: the last customer-facing producers follow the household's language

backup_integrity_ok / backup_integrity_failed now take facts and push bundle
keys (Hungarian bytes unchanged - go-parity, pinned verbatim by
TestR585_IntegrityHungarianIsUnchanged). The interrupted-operation alert
(backup_failed, customer-enabled by default) used to send the operator's
ENGLISH sentence to every household; NotifyInterruptedOperation composes it
per language, the English byte-identical to the operator's log line. The
now-callerless NotifyBackupFailed is removed. local_api_endpoint_drift is
operator-only (no customer toggle) and already English by design - not
changed.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0159rPz1ZhFKsS53msqPYxtS

controller/internal/backup/appstop_marker.go

@@ -62,6 +62,23 @@ func (r AppStopReason) humanReason() string {
 	}
 }
 
+// MessageKey is the bundle key that names this reason in the household's language (R-585), or "" for a
+// reason this build has no sentence for — the caller then shows the raw reason, as humanReason does.
+// Pinned against humanReason by TestR585_InterruptedOperationFollowsTheHousehold (internal/notify): the
+// English bundle text must equal what the operator's log line says.
+func (r AppStopReason) MessageKey() string {
+	switch r {
+	case ReasonVolumeDump:
+		return "appstop.reason.volume_dump"
+	case ReasonOffboxReconstitute:
+		return "appstop.reason.offbox_reconstitute"
+	case ReasonAppExport:
+		return "appstop.reason.app_export"
+	default:
+		return ""
+	}
+}
+
 // AppStopMarker is the persisted "these apps were stopped by an operation that has not reported
 // finishing — they are owed a restart" note.
 type AppStopMarker struct {