refactor: Projektstruktur in app/ und backend/ aufgeteilt

app/lib/models/queued_message.dart

@@ -0,0 +1,51 @@
+class QueuedMessage {
+  final String id;
+  final String topic;
+  final Map<String, dynamic> payload;
+  final DateTime createdAt;
+  final int retryCount;
+
+  QueuedMessage({
+    required this.id,
+    required this.topic,
+    required this.payload,
+    required this.createdAt,
+    this.retryCount = 0,
+  });
+
+  factory QueuedMessage.fromJson(Map<String, dynamic> json) {
+    return QueuedMessage(
+      id: json['id'],
+      topic: json['topic'],
+      payload: Map<String, dynamic>.from(json['payload']),
+      createdAt: DateTime.parse(json['createdAt']),
+      retryCount: json['retryCount'] ?? 0,
+    );
+  }
+
+  Map<String, dynamic> toJson() {
+    return {
+      'id': id,
+      'topic': topic,
+      'payload': payload,
+      'createdAt': createdAt.toIso8601String(),
+      'retryCount': retryCount,
+    };
+  }
+
+  QueuedMessage copyWith({
+    String? id,
+    String? topic,
+    Map<String, dynamic>? payload,
+    DateTime? createdAt,
+    int? retryCount,
+  }) {
+    return QueuedMessage(
+      id: id ?? this.id,
+      topic: topic ?? this.topic,
+      payload: payload ?? this.payload,
+      createdAt: createdAt ?? this.createdAt,
+      retryCount: retryCount ?? this.retryCount,
+    );
+  }
+}