migrated Marianum Message module to the Marianum-Connect API and implemented push notification deep linking

lib/api/demo/data/demo_marianum_message.dart

@@ -1,3 +1,5 @@
+import 'package:intl/intl.dart';
+
 import '../../../state/app/modules/marianum_message/bloc/marianum_message_state.dart';
 
 /// Demo fixtures for the info messages — a single friendly welcome entry so the
@@ -6,16 +8,16 @@ class DemoMarianumMessage {
   const DemoMarianumMessage._();
 
   static MarianumMessageList list() {
-    final today = DateTime.now();
-    final date =
-        '${today.day.toString().padLeft(2, '0')}.${today.month.toString().padLeft(2, '0')}.${today.year}';
+    final date = DateFormat.yMMMM('de').format(DateTime.now());
 
     return MarianumMessageList(
       base: 'https://marianum-fulda.de',
       messages: [
         MarianumMessage(
+          id: 'demo',
           name: 'Willkommen in der Marianum-App',
           date: date,
+          description: 'Eine kurze Begrüßung zum Ausprobieren.',
           url: 'https://marianum-fulda.de',
         ),
       ],