implemented absence report module with form validation, prefill support, and API integration

lib/api/demo/data/demo_absence.dart

@@ -0,0 +1,17 @@
+import '../../marianumconnect/queries/absence/absence_prefill_response.dart';
+
+/// Demo fixtures for the absence-report form: the class dropdown and the
+/// identity/phone prefill. Typed (compile-checked) so a field rename can't
+/// silently drift the demo shape away from what the queries parse.
+class DemoAbsence {
+  const DemoAbsence._();
+
+  static List<String> classes() => const ['5a', '6b', '7c', '9d', '10a', 'Q1'];
+
+  static AbsencePrefillResponse prefill() => AbsencePrefillResponse(
+    firstName: 'Max',
+    lastName: 'Mustermann',
+    className: '10a',
+    phone: '0123 456789',
+  );
+}

lib/api/demo/demo_marianumconnect.dart

@@ -1,3 +1,4 @@
+import 'data/demo_absence.dart';
 import 'data/demo_breaker.dart';
 import 'data/demo_holidays.dart';
 import 'data/demo_timetable.dart';
@@ -39,6 +40,10 @@ class DemoMarianumConnect {
             .toList();
       case 'breaker':
         return DemoBreaker.none().toJson();
+      case 'absence/classes':
+        return DemoAbsence.classes();
+      case 'absence/prefill':
+        return DemoAbsence.prefill().toJson();
       case 'timetable/elements/teachers':
       case 'timetable/elements/students':
       case 'timetable/elements/classes':