refactor: Projektstruktur in app/ und backend/ aufgeteilt

app/lib/entities/chat_message_entity.dart

@@ -0,0 +1,48 @@
+import 'package:objectbox/objectbox.dart';
+
+@Entity()
+class ChatMessageEntity {
+  @Id()
+  int id = 0;
+
+  @Unique()
+  String messageId;
+
+  @Index()
+  String conversationKey;
+
+  String content;
+
+  String contentType; // 'TEXT' or 'IMAGE'
+
+  @Property(type: PropertyType.date)
+  @Index()
+  DateTime createdAt;
+
+  String origin; // 'INCOMING' or 'OUTGOING'
+
+  String messageType; // 'NORMAL', 'JOB_ASSIGNMENT', etc.
+
+  String? jobId;
+
+  String? jobNumber;
+
+  bool read;
+
+  bool pendingSync;
+
+  ChatMessageEntity({
+    required this.messageId,
+    required this.conversationKey,
+    required this.content,
+    this.contentType = 'TEXT',
+    required this.createdAt,
+    required this.origin,
+    required this.messageType,
+    this.jobId,
+    this.jobNumber,
+    this.read = false,
+    this.pendingSync = false,
+  });
+}
+