Refactor and enhance documentation across the Wolf3D project

- Updated library imports to use the correct package paths for consistency.
- Added detailed documentation comments to various classes and methods, improving code readability and maintainability.
- Refined the GameSelectScreen, SpriteGallery, and VgaGallery classes with clearer descriptions of their functionality.
- Enhanced the CliInput class to better explain the input handling process and its interaction with the engine.
- Improved the SixelRasterizer and Opl2Emulator classes with comprehensive comments on their operations and state management.
- Removed the deprecated wolf_3d.dart file and consolidated its functionality into wolf_3d_flutter.dart for a cleaner architecture.
- Updated the Wolf3dFlutterInput class to clarify its role in merging keyboard and pointer events.
- Enhanced the rendering classes to provide better context on their purpose and usage within the Flutter framework.

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

apps/wolf_3d_gui/lib/screens/episode_screen.dart

@@ -1,13 +1,19 @@
+/// Episode picker and asset-browser entry point for the selected game version.
+library;
+
 import 'package:flutter/material.dart';
 import 'package:wolf_3d_dart/wolf_3d_data_types.dart';
-import 'package:wolf_3d_flutter/wolf_3d.dart';
+import 'package:wolf_3d_flutter/wolf_3d_flutter.dart';
 import 'package:wolf_3d_gui/screens/difficulty_screen.dart';
 import 'package:wolf_3d_gui/screens/sprite_gallery.dart';
 import 'package:wolf_3d_gui/screens/vga_gallery.dart';
 
+/// Presents the episode list and shortcuts into the asset gallery screens.
 class EpisodeScreen extends StatefulWidget {
+  /// Shared application facade whose active game must already be set.
   final Wolf3d wolf3d;
 
+  /// Creates the episode-selection screen for [wolf3d].
   const EpisodeScreen({super.key, required this.wolf3d});
 
   @override
@@ -21,6 +27,7 @@ class _EpisodeScreenState extends State<EpisodeScreen> {
     widget.wolf3d.audio.playMenuMusic();
   }
 
+  /// Persists the chosen episode in [Wolf3d] and advances to difficulty select.
   void _selectEpisode(int index) {
     widget.wolf3d.setActiveEpisode(index);
     Navigator.of(context).push(