feat: Add file selector support and enhance game data directory management

Signed-off-by: Hans Kokx <hans.d.kokx@gmail.com>

packages/wolf_3d_flutter/test/game_data_directory_persistence_test.dart

@@ -51,7 +51,7 @@ void main() {
       });
 
       final persistence = DefaultGameDataDirectoryPersistence(
-        filePath: '${tempDir.path}/data_source.json',
+        filePath: '${tempDir.path}/settings.json',
       );
 
       await persistence.saveDataDirectory('/tmp/wolf-data');
@@ -70,7 +70,7 @@ void main() {
         }
       });
 
-      final path = '${tempDir.path}/data_source.json';
+      final path = '${tempDir.path}/settings.json';
       final persistence = DefaultGameDataDirectoryPersistence(filePath: path);
 
       await persistence.saveDataDirectory('/tmp/wolf-data');
@@ -79,6 +79,39 @@ void main() {
       expect(await File(path).exists(), isFalse);
       expect(await persistence.loadDataDirectory(), isNull);
     });
+
+    test('preserves unrelated settings when updating data directory', () async {
+      final tempDir = await Directory.systemTemp.createTemp(
+        'wolf3d-data-config-',
+      );
+      addTearDown(() async {
+        if (await tempDir.exists()) {
+          await tempDir.delete(recursive: true);
+        }
+      });
+
+      final path = '${tempDir.path}/settings.json';
+      final file = File(path);
+      await file.parent.create(recursive: true);
+      await file.writeAsString(
+        '{"renderScale":2.0,"preferSoftwareRenderer":false}',
+      );
+
+      final persistence = DefaultGameDataDirectoryPersistence(filePath: path);
+
+      await persistence.saveDataDirectory('/tmp/wolf-data');
+
+      final updated = await file.readAsString();
+      expect(updated, contains('"renderScale":2.0'));
+      expect(updated, contains('"preferSoftwareRenderer":false'));
+      expect(updated, contains('"dataDirectory":"/tmp/wolf-data"'));
+
+      await persistence.saveDataDirectory(null);
+      final cleared = await file.readAsString();
+      expect(cleared, contains('"renderScale":2.0'));
+      expect(cleared, contains('"preferSoftwareRenderer":false'));
+      expect(cleared.contains('"dataDirectory"'), isFalse);
+    });
   });
 
   testWidgets('Wolf3dApp forwards configured directory to no-data screen', (