Refactor: reorganize scripts with domain-driven design structure

Move all C# scripts from flat structure to organized folders:
- Core/ for game logic (Game, GameState, GameSettings)
- UI/Menus/ and UI/Dialogs/ for user interface
- Systems/ for reusable systems (Save, Localization)
- Data/ for data models and configuration
- Added framework for future: Gameplay/, Story/, Modding/

Update all .tscn scene files to reference new script paths.
Fix timing issue in AdvancedSaveDialog focus handling.

scripts/UI/Menus/MainMenu.cs

@@ -0,0 +1,88 @@
+using Godot;
+
+namespace TheGame
+{
+    public partial class MainMenu : Control
+    {
+        private Button _loadButton;
+        private Label _titleLabel;
+        private Button _startButton;
+        private Button _settingsButton;
+        private Button _exitButton;
+        
+        public override void _Ready()
+        {
+            // Lägg till i localized_ui gruppen
+            AddToGroup("localized_ui");
+            
+            _loadButton = GetNode<Button>("VBoxContainer/LoadButton");
+            _titleLabel = GetNode<Label>("VBoxContainer/TitleLabel");
+            _startButton = GetNode<Button>("VBoxContainer/StartButton");
+            _settingsButton = GetNode<Button>("VBoxContainer/SettingsButton");
+            _exitButton = GetNode<Button>("VBoxContainer/ExitButton");
+            
+            // Initiera inställningar och språk
+            GameSettings.Instance.ApplyAllSettings();
+            
+            UpdateLoadButtonState();
+            UpdateLocalization();
+        }
+        
+        public void UpdateLocalization()
+        {
+            var loc = LocalizationManager.Instance;
+            _titleLabel.Text = loc.GetText("main_menu_title");
+            _startButton.Text = loc.GetText("main_menu_start");
+            _loadButton.Text = loc.GetText("main_menu_load");
+            _settingsButton.Text = loc.GetText("main_menu_settings");
+            _exitButton.Text = loc.GetText("main_menu_exit");
+        }
+        
+        private void UpdateLoadButtonState()
+        {
+            // Kontrollera om det finns sparade spel
+            var saveManager = new SaveManager();
+            var savedGames = saveManager.GetSavedGames();
+            _loadButton.Disabled = savedGames.Count == 0;
+        }
+        
+        private void _on_start_button_pressed()
+        {
+            // Rensa befintligt game state för att starta nytt spel
+            GameState.ResetGameState();
+            
+            GetTree().ChangeSceneToFile("res://scenes/Game.tscn");
+        }
+        
+        public override void _Notification(int what)
+        {
+            if (what == NotificationWMCloseRequest)
+            {
+                // I huvudmenyn kan vi avsluta direkt
+                GetTree().Quit();
+            }
+        }
+        
+        private void _on_load_button_pressed()
+        {
+            GetTree().ChangeSceneToFile("res://scenes/LoadGameMenu.tscn");
+        }
+        
+        private void _on_settings_button_pressed()
+        {
+            // Skapa settings menu som popup
+            var settingsScene = GD.Load<PackedScene>("res://scenes/SettingsMenu.tscn");
+            var settingsMenu = settingsScene.Instantiate<SettingsMenu>();
+            
+            // Sätt process mode för main menu context
+            settingsMenu.ProcessMode = ProcessModeEnum.Always;
+            
+            GetTree().Root.AddChild(settingsMenu);
+        }
+        
+        private void _on_exit_button_pressed()
+        {
+            GetTree().Quit();
+        }
+    }
+}