refactor: Projektstruktur in app/ und backend/ aufgeteilt

app/lib/entities/photo_entity.dart

@@ -0,0 +1,23 @@
+import 'package:objectbox/objectbox.dart';
+
+@Entity()
+class PhotoEntity {
+  @Id()
+  int id = 0;
+
+  String taskId;
+
+  int photoIndex;
+
+  String data; // Base64-encoded photo data
+
+  @Property(type: PropertyType.date)
+  DateTime createdAt;
+
+  PhotoEntity({
+    required this.taskId,
+    required this.photoIndex,
+    required this.data,
+    required this.createdAt,
+  });
+}