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/game_screen.dart

@@ -1,3 +1,6 @@
+/// Active gameplay screen for the Flutter host.
+library;
+
 import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
 import 'package:wolf_3d_dart/wolf_3d_data_types.dart';
@@ -6,13 +9,24 @@ import 'package:wolf_3d_flutter/wolf_3d_input_flutter.dart';
 import 'package:wolf_3d_renderer/wolf_3d_ascii_renderer.dart';
 import 'package:wolf_3d_renderer/wolf_3d_flutter_renderer.dart';
 
+/// Owns a [WolfEngine] instance and exposes renderer/input integrations to Flutter.
 class GameScreen extends StatefulWidget {
+  /// Fully parsed game data for the selected version.
   final WolfensteinData data;
+
+  /// Difficulty applied when creating the engine session.
   final Difficulty difficulty;
+
+  /// Episode index used as the starting world.
   final int startingEpisode;
+
+  /// Shared audio backend reused across menu and gameplay screens.
   final EngineAudio audio;
+
+  /// Flutter input adapter that translates widget events into engine input.
   final Wolf3dFlutterInput input;
 
+  /// Creates a gameplay screen with the supplied game session configuration.
   const GameScreen({
     required this.data,
     required this.difficulty,
@@ -55,6 +69,8 @@ class _GameScreenState extends State<GameScreen> {
         onPointerHover: widget.input.onPointerMove,
         child: Stack(
           children: [
+            // Keep both renderers behind the same engine so mode switching does
+            // not reset level state or audio playback.
             _useAsciiMode
                 ? WolfAsciiRenderer(engine: _engine)
                 : WolfFlutterRenderer(engine: _engine),
@@ -80,7 +96,7 @@ class _GameScreenState extends State<GameScreen> {
                 ),
               ),
 
-            // TAB listener
+            // Tab toggles the renderer implementation for quick visual debugging.
             Focus(
               autofocus: true,
               onKeyEvent: (node, event) {
@@ -94,7 +110,8 @@ class _GameScreenState extends State<GameScreen> {
               child: const SizedBox.shrink(),
             ),
 
-            // Loading Overlay
+            // A second full-screen overlay keeps the presentation simple while
+            // the engine is still warming up or decoding the first frame.
             if (!_engine.isInitialized)
               Container(
                 color: Colors.black,