Refactor menu structure and add Flutter-specific input and persistence layers

- Moved menu-related classes to a new structure under `src/menu/`.
- Introduced `WolfMenuPresentation` to handle menu art and mappings.
- Added `MenuManager` tests to ensure menu state reflects game status.
- Implemented `FlutterRendererSettingsPersistence` and `FlutterSaveGamePersistence` for managing settings and save files on desktop platforms.
- Created `Wolf3dFlutterInput` to handle keyboard and mouse input in a Flutter environment.
- Updated README to reflect new package structure and usage instructions.

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

packages/wolf_3d_flutter/lib/persistence/renderer_settings_persistence_flutter.dart

@@ -0,0 +1,75 @@
+/// Flutter host adapter for persisting renderer settings to a local file.
+///
+/// Uses `dart:io` for desktop targets where a writable path is available.
+/// On web and other platforms that lack dart:io, persistence is silently
+/// skipped so the rest of the app continues to work normally.
+library;
+
+import 'dart:io';
+
+import 'package:flutter/foundation.dart';
+import 'package:wolf_3d_dart/wolf_3d_engine.dart';
+
+/// Persists [WolfRendererSettings] as JSON to the app's support directory.
+///
+/// This implementation relies on `dart:io` and is therefore only active on
+/// non-web platforms.  Pass an explicit [filePath] during testing.
+class FlutterRendererSettingsPersistence extends RendererSettingsPersistence
+    with JsonRendererSettingsPersistence {
+  FlutterRendererSettingsPersistence({String? filePath}) : _filePath = filePath;
+
+  final String? _filePath;
+  String? _resolvedPath;
+
+  String get filePath {
+    if (_resolvedPath != null) {
+      return _resolvedPath!;
+    }
+    if (_filePath != null) {
+      _resolvedPath = _filePath;
+      return _resolvedPath!;
+    }
+    _resolvedPath = '$platformConfigDir/settings.json';
+    return _resolvedPath!;
+  }
+
+  @override
+  Future<String?> readRaw() async {
+    if (kIsWeb) return null;
+    try {
+      final File f = File(filePath);
+      if (!f.existsSync()) return null;
+      return await f.readAsString();
+    } catch (_) {
+      return null;
+    }
+  }
+
+  @override
+  Future<void> writeRaw(String json) async {
+    if (kIsWeb) return;
+    try {
+      await File(filePath).writeAsString(json, flush: true);
+    } catch (_) {
+      // Best-effort.
+    }
+  }
+
+  String get platformConfigDir {
+    if (Platform.isLinux) {
+      final String xdg = Platform.environment['XDG_CONFIG_HOME'] ?? '';
+      final String home = Platform.environment['HOME'] ?? '.';
+      return xdg.isNotEmpty ? '$xdg/wolf3d' : '$home/.config/wolf3d';
+    }
+    if (Platform.isMacOS) {
+      final String home = Platform.environment['HOME'] ?? '.';
+      return '$home/Library/Application Support/wolf3d';
+    }
+    if (Platform.isWindows) {
+      final String appData = Platform.environment['APPDATA'] ?? '.';
+      return '$appData/wolf3d';
+    }
+    final String home = Platform.environment['HOME'] ?? '.';
+    return '$home/.config/wolf3d';
+  }
+}

packages/wolf_3d_flutter/lib/persistence/save_game_persistence_flutter.dart

@@ -0,0 +1,112 @@
+library;
+
+import 'dart:io';
+
+import 'package:flutter/foundation.dart';
+import 'package:wolf_3d_dart/wolf_3d_data_types.dart';
+import 'package:wolf_3d_dart/wolf_3d_engine.dart';
+
+/// Flutter desktop adapter for slot-based game save persistence.
+class FlutterSaveGamePersistence implements SaveGamePersistence {
+  FlutterSaveGamePersistence({String? directoryPath})
+    : _directoryPath = directoryPath;
+
+  final String? _directoryPath;
+  String? _resolvedDirectoryPath;
+
+  Future<String> _resolveDirectoryPath() async {
+    if (_resolvedDirectoryPath != null) {
+      return _resolvedDirectoryPath!;
+    }
+
+    if (_directoryPath != null) {
+      _resolvedDirectoryPath = _directoryPath;
+      return _resolvedDirectoryPath!;
+    }
+
+    _resolvedDirectoryPath = '${_platformConfigDir()}/saves';
+    return _resolvedDirectoryPath!;
+  }
+
+  @override
+  Future<Uint8List?> load({
+    required int slot,
+    required GameVersion version,
+  }) async {
+    if (kIsWeb) {
+      return null;
+    }
+
+    try {
+      final String dirPath = await _resolveDirectoryPath();
+      final File file = File(_slotPath(dirPath, slot, version));
+      if (!file.existsSync()) {
+        return null;
+      }
+      return await file.readAsBytes();
+    } catch (_) {
+      return null;
+    }
+  }
+
+  @override
+  Future<bool> exists({
+    required int slot,
+    required GameVersion version,
+  }) async {
+    if (kIsWeb) {
+      return false;
+    }
+
+    try {
+      final String dirPath = await _resolveDirectoryPath();
+      final File file = File(_slotPath(dirPath, slot, version));
+      return file.existsSync() && file.lengthSync() > 0;
+    } catch (_) {
+      return false;
+    }
+  }
+
+  @override
+  Future<void> save({
+    required int slot,
+    required GameVersion version,
+    required Uint8List bytes,
+  }) async {
+    if (kIsWeb) {
+      return;
+    }
+
+    final String dirPath = await _resolveDirectoryPath();
+    final Directory dir = Directory(dirPath);
+    if (!dir.existsSync()) {
+      await dir.create(recursive: true);
+    }
+    await File(
+      _slotPath(dirPath, slot, version),
+    ).writeAsBytes(bytes, flush: true);
+  }
+
+  String _slotPath(String dirPath, int slot, GameVersion version) {
+    final String normalizedSlot = slot.clamp(0, 9).toString();
+    return '$dirPath/SAVEGAM$normalizedSlot.${version.fileExtension}';
+  }
+}
+
+String _platformConfigDir() {
+  if (Platform.isLinux) {
+    final String xdg = Platform.environment['XDG_CONFIG_HOME'] ?? '';
+    final String home = Platform.environment['HOME'] ?? '.';
+    return xdg.isNotEmpty ? '$xdg/wolf3d' : '$home/.config/wolf3d';
+  }
+  if (Platform.isMacOS) {
+    final String home = Platform.environment['HOME'] ?? '.';
+    return '$home/Library/Application Support/wolf3d';
+  }
+  if (Platform.isWindows) {
+    final String appData = Platform.environment['APPDATA'] ?? '.';
+    return '$appData/wolf3d';
+  }
+  final String home = Platform.environment['HOME'] ?? '.';
+  return '$home/.config/wolf3d';
+}