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>

apps/wolf_3d_gui/lib/main.dart

@@ -6,7 +6,7 @@ library;
 
 import 'package:flutter/material.dart';
 import 'package:wolf_3d_flutter/wolf_3d_flutter.dart';
-import 'package:wolf_3d_gui/screens/game_select_screen.dart';
+import 'package:wolf_3d_gui/screens/game_screen.dart';
 
 /// Creates the application shell after loading available Wolf3D data sets.
 void main() async {
@@ -16,7 +16,65 @@ void main() async {
 
   runApp(
     MaterialApp(
-      home: GameSelectScreen(wolf3d: wolf3d),
+      home: wolf3d.availableGames.isEmpty
+          ? const _NoGameDataScreen()
+          : GameScreen(wolf3d: wolf3d),
     ),
   );
 }
+
+class _NoGameDataScreen extends StatelessWidget {
+  const _NoGameDataScreen();
+
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      backgroundColor: const Color(0xFF140000),
+      body: Center(
+        child: Padding(
+          padding: const EdgeInsets.all(24),
+          child: ConstrainedBox(
+            constraints: const BoxConstraints(maxWidth: 640),
+            child: DecoratedBox(
+              decoration: BoxDecoration(
+                color: const Color(0xFF590002),
+                border: Border.all(color: const Color(0xFFB00000), width: 2),
+              ),
+              child: const Padding(
+                padding: EdgeInsets.all(20),
+                child: Column(
+                  mainAxisSize: MainAxisSize.min,
+                  crossAxisAlignment: CrossAxisAlignment.start,
+                  children: [
+                    Text(
+                      'WOLF3D DATA NOT FOUND',
+                      style: TextStyle(
+                        color: Color(0xFFFFF700),
+                        fontSize: 24,
+                        fontWeight: FontWeight.bold,
+                      ),
+                    ),
+                    SizedBox(height: 16),
+                    Text(
+                      'No game files were discovered.\n\n'
+                      'Add Wolfenstein 3D data files to one of these locations:\n'
+                      '- packages/wolf_3d_assets/assets/retail\n'
+                      '- packages/wolf_3d_assets/assets/shareware\n'
+                      '- or a discoverable local game-data folder.\n\n'
+                      'Restart the app after adding the files.',
+                      style: TextStyle(
+                        color: Colors.white,
+                        fontSize: 15,
+                        height: 1.4,
+                      ),
+                    ),
+                  ],
+                ),
+              ),
+            ),
+          ),
+        ),
+      ),
+    );
+  }
+}