fix(geplante-nachrichten): distinguish unconfigured bot from unreachable Nextcloud in room picker

backend/src/services/scheduledMessages.service.ts

@@ -37,6 +37,7 @@ interface RoomInfo {
 interface RoomsResult {
   configured: boolean;
   data?: RoomInfo[];
+  error?: string;
 }
 
 // ── Helpers ──────────────────────────────────────────────────────────────────
@@ -327,7 +328,7 @@ async function getRooms(): Promise<RoomsResult> {
     logger.error('scheduledMessages.getRooms failed', {
       error: error instanceof Error ? error.message : String(error),
     });
-    return { configured: false };
+    return { configured: true, data: [], error: 'Verbindung zu Nextcloud fehlgeschlagen' };
   }
 }