Moved all widgets and logic from gui app to Flutter package

- Implemented DebugToolsScreen for navigation to asset galleries.
- Created GameScreen to manage gameplay and renderer integrations.
- Added NoGameDataScreen to handle scenarios with missing game data.
- Developed SpriteGallery for visual browsing of sprite assets.
- Introduced VgaGallery for displaying VGA images from game data.
- Added GalleryGameSelector widget for selecting game variants in galleries.
- Created Wolf3dApp as the main application shell for managing game states.
- Implemented WolfMenuShell for consistent menu layouts across screens.
- Enhanced Wolf3d class to support debug mode and related functionalities.
- Updated pubspec.yaml to include window_manager dependency.
- Added tests for game screen lifecycle and debug mode functionalities.

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

packages/wolf_3d_flutter/lib/widgets/gallery_game_selector.dart

@@ -0,0 +1,61 @@
+library;
+
+import 'package:flutter/material.dart';
+import 'package:wolf_3d_dart/wolf_3d_data_types.dart';
+import 'package:wolf_3d_flutter/wolf_3d_flutter.dart';
+
+/// Human-readable title for a game variant in gallery selectors.
+String formatGalleryGameTitle(GameVersion version) {
+  switch (version) {
+    case GameVersion.shareware:
+      return 'SHAREWARE';
+    case GameVersion.retail:
+      return 'RETAIL';
+    case GameVersion.spearOfDestiny:
+      return 'SPEAR OF DESTINY';
+    case GameVersion.spearOfDestinyDemo:
+      return 'SOD DEMO';
+  }
+}
+
+/// Selects which discovered game data set gallery screens should display.
+class GalleryGameSelector extends StatelessWidget {
+  final Wolf3d wolf3d;
+  final WolfensteinData selectedGame;
+  final ValueChanged<WolfensteinData> onSelected;
+
+  const GalleryGameSelector({
+    super.key,
+    required this.wolf3d,
+    required this.selectedGame,
+    required this.onSelected,
+  });
+
+  @override
+  Widget build(BuildContext context) {
+    return Padding(
+      padding: const EdgeInsets.only(right: 12),
+      child: Center(
+        child: DropdownButtonHideUnderline(
+          child: DropdownButton<WolfensteinData>(
+            value: selectedGame,
+            borderRadius: BorderRadius.circular(8),
+            dropdownColor: Theme.of(context).colorScheme.surface,
+            iconEnabledColor: Theme.of(context).colorScheme.onSurface,
+            onChanged: (WolfensteinData? game) {
+              if (game != null) {
+                onSelected(game);
+              }
+            },
+            items: wolf3d.availableGames.map((WolfensteinData game) {
+              return DropdownMenuItem<WolfensteinData>(
+                value: game,
+                child: Text(formatGalleryGameTitle(game.version)),
+              );
+            }).toList(),
+          ),
+        ),
+      ),
+    );
+  }
+}

packages/wolf_3d_flutter/lib/widgets/wolf3d_app.dart

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+library;
+
+import 'package:flutter/material.dart';
+import 'package:wolf_3d_flutter/wolf_3d_flutter.dart';
+
+/// Minimal app shell that binds a prepared [Wolf3d] instance to host screens.
+class Wolf3dApp extends StatelessWidget {
+  /// Shared initialized facade that owns game data, input, and audio services.
+  final Wolf3d wolf3d;
+
+  const Wolf3dApp({
+    super.key,
+    required this.wolf3d,
+  });
+
+  @override
+  Widget build(BuildContext context) {
+    return wolf3d.availableGames.isEmpty
+        ? const NoGameDataScreen()
+        : GameScreen(wolf3d: wolf3d);
+  }
+}

packages/wolf_3d_flutter/lib/widgets/wolf_menu_shell.dart

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+/// Shared shell for Wolf3D-style menu screens.
+library;
+
+import 'package:flutter/material.dart';
+import 'package:wolf_3d_dart/wolf_3d_data_types.dart';
+import 'package:wolf_3d_flutter/renderer/wolf_3d_asset_painter.dart';
+
+/// Provides a common menu layout with panel framing and optional bottom art.
+class WolfMenuShell extends StatelessWidget {
+  /// Full-screen background color behind the panel.
+  final Color backgroundColor;
+
+  /// Solid panel fill used for the menu content area.
+  final Color panelColor;
+
+  /// Optional heading shown above the panel (text or image).
+  final Widget? header;
+
+  /// Primary menu content rendered inside the panel.
+  final Widget panelChild;
+
+  /// Optional centered VGA image anchored near the bottom of the screen.
+  final VgaImage? bottomSprite;
+
+  /// Width of the menu panel.
+  final double panelWidth;
+
+  /// Padding applied around [panelChild] inside the panel.
+  final EdgeInsets panelPadding;
+
+  /// Scale factor for [bottomSprite].
+  final double bottomSpriteScale;
+
+  /// Distance from the bottom edge for [bottomSprite].
+  final double bottomOffset;
+
+  /// Vertical spacing between [header] and the panel.
+  final double headerSpacing;
+
+  const WolfMenuShell({
+    super.key,
+    required this.backgroundColor,
+    required this.panelColor,
+    required this.panelChild,
+    this.header,
+    this.bottomSprite,
+    this.panelWidth = 520,
+    this.panelPadding = const EdgeInsets.symmetric(
+      horizontal: 20,
+      vertical: 16,
+    ),
+    this.bottomSpriteScale = 3,
+    this.bottomOffset = 20,
+    this.headerSpacing = 14,
+  });
+
+  @override
+  Widget build(BuildContext context) {
+    return Stack(
+      children: [
+        Positioned.fill(
+          child: ColoredBox(color: backgroundColor),
+        ),
+        Center(
+          child: Column(
+            mainAxisSize: MainAxisSize.min,
+            children: [
+              if (header case final Widget value) value,
+              if (header != null) SizedBox(height: headerSpacing),
+              Container(
+                width: panelWidth,
+                padding: panelPadding,
+                color: panelColor,
+                child: panelChild,
+              ),
+            ],
+          ),
+        ),
+        if (bottomSprite != null)
+          Positioned(
+            left: 0,
+            right: 0,
+            bottom: bottomOffset,
+            child: Center(
+              child: SizedBox(
+                width: bottomSprite!.width * bottomSpriteScale,
+                height: bottomSprite!.height * bottomSpriteScale,
+                child: WolfAssetPainter.vga(bottomSprite),
+              ),
+            ),
+          ),
+      ],
+    );
+  }
+}