feat(frontend): add GROUP_HAS_ACTIVE_INVITES error code + i18n keys

Adds the error code to the ErrorCode union and getErrorMessage() switch.
Adds admin_new_invite_groups, admin_invite_groups_load_error, and
error_group_has_active_invites to all three locale files (de/en/es).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/messages/de.json

@@ -706,6 +706,7 @@
 	"error_invite_exhausted": "Dieser Einladungslink wurde bereits vollständig verwendet.",
 	"error_invite_revoked": "Dieser Einladungslink wurde deaktiviert.",
 	"error_invite_expired": "Dieser Einladungslink ist abgelaufen.",
+	"error_group_has_active_invites": "Diese Gruppe kann nicht gelöscht werden, da sie in einer aktiven Einladung verwendet wird.",
 	"register_heading": "Konto erstellen",
 	"register_subtext": "Du wurdest eingeladen, dem Familienarchiv beizutreten.",
 	"register_label_first_name": "Vorname",
@@ -765,6 +766,8 @@
 	"admin_new_invite_prefill_last": "Nachname vorausfüllen (optional)",
 	"admin_new_invite_prefill_email": "E-Mail vorausfüllen (optional)",
 	"admin_new_invite_expires": "Ablaufdatum (optional)",
+	"admin_new_invite_groups": "Gruppen (optional)",
+	"admin_invite_groups_load_error": "Gruppen konnten nicht geladen werden. Die Einladung kann ohne Gruppenauswahl erstellt werden.",
 	"admin_invite_created_title": "Einladung erstellt",
 	"admin_invite_created_desc": "Teile diesen Link mit der einzuladenden Person:",
 	"admin_invite_revoke_confirm": "Einladung wirklich widerrufen?",

frontend/messages/en.json

@@ -706,6 +706,7 @@
 	"error_invite_exhausted": "This invite link has already been fully used.",
 	"error_invite_revoked": "This invite link has been deactivated.",
 	"error_invite_expired": "This invite link has expired.",
+	"error_group_has_active_invites": "This group cannot be deleted because it is referenced by one or more active invite links.",
 	"register_heading": "Create account",
 	"register_subtext": "You've been invited to join Familienarchiv.",
 	"register_label_first_name": "First name",
@@ -765,6 +766,8 @@
 	"admin_new_invite_prefill_last": "Pre-fill last name (optional)",
 	"admin_new_invite_prefill_email": "Pre-fill email (optional)",
 	"admin_new_invite_expires": "Expiry date (optional)",
+	"admin_new_invite_groups": "Groups (optional)",
+	"admin_invite_groups_load_error": "Groups could not be loaded. The invite can still be created without group assignment.",
 	"admin_invite_created_title": "Invite created",
 	"admin_invite_created_desc": "Share this link with the person you are inviting:",
 	"admin_invite_revoke_confirm": "Really revoke this invite?",

frontend/messages/es.json

@@ -706,6 +706,7 @@
 	"error_invite_exhausted": "Este enlace de invitación ya ha sido completamente utilizado.",
 	"error_invite_revoked": "Este enlace de invitación ha sido desactivado.",
 	"error_invite_expired": "Este enlace de invitación ha expirado.",
+	"error_group_has_active_invites": "Este grupo no puede eliminarse porque está referenciado por uno o más enlaces de invitación activos.",
 	"register_heading": "Crear cuenta",
 	"register_subtext": "Has sido invitado a unirte al Familienarchiv.",
 	"register_label_first_name": "Nombre",
@@ -765,6 +766,8 @@
 	"admin_new_invite_prefill_last": "Prellenar apellido (opcional)",
 	"admin_new_invite_prefill_email": "Prellenar correo (opcional)",
 	"admin_new_invite_expires": "Fecha de vencimiento (opcional)",
+	"admin_new_invite_groups": "Grupos (opcional)",
+	"admin_invite_groups_load_error": "No se pudieron cargar los grupos. La invitación puede crearse sin asignar grupos.",
 	"admin_invite_created_title": "Invitación creada",
 	"admin_invite_created_desc": "Comparte este enlace con la persona invitada:",
 	"admin_invite_revoke_confirm": "¿Realmente revocar esta invitación?",

frontend/src/lib/shared/errors.ts

@@ -22,6 +22,7 @@ export type ErrorCode =
 	| 'INVITE_EXHAUSTED'
 	| 'INVITE_REVOKED'
 	| 'INVITE_EXPIRED'
+	| 'GROUP_HAS_ACTIVE_INVITES'
 	| 'ANNOTATION_NOT_FOUND'
 	| 'ANNOTATION_UPDATE_FAILED'
 	| 'TRANSCRIPTION_BLOCK_NOT_FOUND'
@@ -108,6 +109,8 @@ export function getErrorMessage(code: ErrorCode | string | undefined): string {
 			return m.error_invite_revoked();
 		case 'INVITE_EXPIRED':
 			return m.error_invite_expired();
+		case 'GROUP_HAS_ACTIVE_INVITES':
+			return m.error_group_has_active_invites();
 		case 'ANNOTATION_NOT_FOUND':
 			return m.error_annotation_not_found();
 		case 'ANNOTATION_UPDATE_FAILED':