feat: Enhance GameDataPickerManager and Wolf3dAppManager with improved directory and file picking capabilities

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

packages/wolf_3d_flutter/lib/wolf_3d_flutter.dart

@@ -83,6 +83,14 @@ class Wolf3dFlutterEngine extends Wolf3dEngine {
   }
 
   /// Initializes the engine by loading available game data.
+  ///
+  /// If [directory] is provided, it is persisted and treated as the primary
+  /// external search root. If omitted, a previously persisted directory is
+  /// used when available. [additionalDirectories] are scanned after the
+  /// primary directory and are not persisted.
+  ///
+  /// This method merges bundled package data (when present) with discovered
+  /// external directories, deduplicating versions by [GameVersion].
   Future<Wolf3dFlutterEngine> init({
     String? directory,
     Iterable<String>? additionalDirectories,