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/Systems/Save/SaveInstance.cs

@@ -0,0 +1,57 @@
+using System;
+
+namespace TheGame
+{
+    public class SaveInstance
+    {
+        public string InstanceId { get; set; }
+        public float GameTime { get; set; }
+        public DateTime SaveDate { get; set; }
+        public string DisplayName { get; set; }
+        public bool IsAutoSave { get; set; } = false;
+        
+        public SaveInstance()
+        {
+            InstanceId = Guid.NewGuid().ToString("N")[..8]; // 8-tecken ID
+            SaveDate = DateTime.Now;
+            DisplayName = $"Save {SaveDate:HH:mm:ss}";
+        }
+        
+        public SaveInstance(float gameTime, string displayName = "", bool isAutoSave = false)
+        {
+            InstanceId = Guid.NewGuid().ToString("N")[..8];
+            GameTime = gameTime;
+            SaveDate = DateTime.Now;
+            IsAutoSave = isAutoSave;
+            
+            if (string.IsNullOrEmpty(displayName))
+            {
+                if (isAutoSave)
+                {
+                    DisplayName = $"Auto-save {SaveDate:HH:mm:ss}";
+                }
+                else
+                {
+                    DisplayName = $"Save {SaveDate:HH:mm:ss}";
+                }
+            }
+            else
+            {
+                DisplayName = displayName;
+            }
+        }
+        
+        public string GetFormattedGameTime()
+        {
+            int hours = (int)(GameTime / 3600);
+            int minutes = (int)((GameTime % 3600) / 60);
+            int seconds = (int)(GameTime % 60);
+            return $"{hours:D2}:{minutes:D2}:{seconds:D2}";
+        }
+        
+        public override string ToString()
+        {
+            return $"{DisplayName} - {GetFormattedGameTime()} ({SaveDate:yyyy-MM-dd HH:mm:ss})";
+        }
+    }
+}