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/lib/wolf_3d_flutter.dart

@@ -83,6 +83,7 @@ class Wolf3dFlutterEngine extends Wolf3dEngine {
   /// Initializes the engine by loading available game data.
   Future<Wolf3dFlutterEngine> init({
     String? directory,
+    Iterable<String>? additionalDirectories,
   }) async {
     await desktop_windowing_support.ensureDesktopWindowingInitialized();
     await audio.init();
@@ -128,21 +129,37 @@ class Wolf3dFlutterEngine extends Wolf3dEngine {
       }
     }
 
-    // On non-web platforms, also scan the local filesystem for user-supplied
-    // data folders so the host can pick up extra versions automatically.
-    if (!kIsWeb && resolvedDirectory != null) {
-      try {
-        final externalGames = await WolfensteinLoader.discover(
-          directoryPath: resolvedDirectory,
-          recursive: true,
-        );
-        for (var entry in externalGames.entries) {
-          if (!availableGames.any((g) => g.version == entry.key)) {
-            availableGames.add(entry.value);
-          }
+    // On non-web platforms, also scan local filesystem locations for
+    // user-supplied data folders so the host can pick up extra versions.
+    final Set<String> directoriesToScan = <String>{};
+    if (resolvedDirectory != null && resolvedDirectory.isNotEmpty) {
+      directoriesToScan.add(resolvedDirectory);
+    }
+
+    if (additionalDirectories != null) {
+      for (final String directoryPath in additionalDirectories) {
+        final String trimmedPath = directoryPath.trim();
+        if (trimmedPath.isNotEmpty) {
+          directoriesToScan.add(trimmedPath);
+        }
+      }
+    }
+
+    if (!kIsWeb && directoriesToScan.isNotEmpty) {
+      for (final String directoryPath in directoriesToScan) {
+        try {
+          final externalGames = await WolfensteinLoader.discover(
+            directoryPath: directoryPath,
+            recursive: true,
+          );
+          for (var entry in externalGames.entries) {
+            if (!availableGames.any((g) => g.version == entry.key)) {
+              availableGames.add(entry.value);
+            }
+          }
+        } catch (e) {
+          debugPrint("External discovery failed: $e");
         }
-      } catch (e) {
-        debugPrint("External discovery failed: $e");
       }
     }