Refactor menu rendering and improve projection sampling

- Updated AsciiRasterizer to support game and episode selection menus with improved layout and cursor handling.
- Enhanced SixelRasterizer and SoftwareRasterizer to modularize menu drawing logic for game and episode selection.
- Introduced new methods for drawing menus and applying fade effects across rasterizers.
- Adjusted wall texture sampling in Rasterizer to anchor to projection height center for consistent rendering.
- Added tests for wall texture sampling behavior to ensure legacy compatibility and new functionality.
- Modified Flutter audio adapter to use nullable access for active game and adjusted game selection logic in the main class.
- Cleaned up input handling in Wolf3dFlutterInput by removing unused menu tap variables.

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

packages/wolf_3d_flutter/lib/wolf_3d_flutter.dart

@@ -40,12 +40,15 @@ class Wolf3d {
     return _activeGame!;
   }
 
+  /// Nullable access to the selected game, useful during menu bootstrap.
+  WolfensteinData? get maybeActiveGame => _activeGame;
+
   // Episode selection lives on the facade so menus can configure gameplay
   // before constructing a new engine instance.
-  int _activeEpisode = 0;
+  int? _activeEpisode;
 
   /// Index of the episode currently selected in the UI flow.
-  int get activeEpisode => _activeEpisode;
+  int? get activeEpisode => _activeEpisode;
 
   Difficulty? _activeDifficulty;
 
@@ -80,16 +83,30 @@ class Wolf3d {
   /// engine so it can be retrieved via [engine]. [onGameWon] is invoked when
   /// the player completes the final level of the episode.
   WolfEngine launchEngine({required void Function() onGameWon}) {
+    if (availableGames.isEmpty) {
+      throw StateError(
+        'No game data was discovered. Add game files before launching the engine.',
+      );
+    }
+
     _engine = WolfEngine(
-      data: activeGame,
+      availableGames: availableGames,
       difficulty: _activeDifficulty,
       startingEpisode: _activeEpisode,
       frameBuffer: FrameBuffer(320, 200),
       menuBackgroundRgb: menuBackgroundRgb,
       menuPanelRgb: menuPanelRgb,
-      audio: audio,
+      engineAudio: audio,
       input: input,
       onGameWon: onGameWon,
+      onMenuExit: onGameWon,
+      onGameSelected: (game) {
+        _activeGame = game;
+        audio.activeGame = game;
+      },
+      onEpisodeSelected: (episodeIndex) {
+        _activeEpisode = episodeIndex;
+      },
     );
     _engine!.init();
     return _engine!;
@@ -107,8 +124,18 @@ class Wolf3d {
     _activeEpisode = episodeIndex;
   }
 
+  /// Clears any selected episode so menu flow starts fresh.
+  void clearActiveEpisode() {
+    _activeEpisode = null;
+  }
+
   /// Convenience access to the active episode's level list.
-  List<WolfLevel> get levels => activeGame.episodes[activeEpisode].levels;
+  List<WolfLevel> get levels {
+    if (_activeEpisode == null) {
+      throw StateError('No active episode selected.');
+    }
+    return activeGame.episodes[_activeEpisode!].levels;
+  }
 
   /// Convenience access to the active game's wall textures.
   List<Sprite> get walls => activeGame.walls;
@@ -141,6 +168,7 @@ class Wolf3d {
     }
 
     _activeGame = game;
+    _activeEpisode = null;
     audio.activeGame = game;
   }