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/Core/GameState.cs

@@ -0,0 +1,37 @@
+using Godot;
+
+namespace TheGame
+{
+    public static class GameState
+    {
+        public static float LoadedGameTime = -1;
+        public static GameSeed CurrentGameSeed = null;
+        public static SaveInstance LoadedInstance = null;
+        public static bool HasUnsavedProgress = false;
+        public static float LastSavedGameTime = 0;
+        
+        public static void MarkProgressAsSaved(float gameTime)
+        {
+            LastSavedGameTime = gameTime;
+            HasUnsavedProgress = false;
+        }
+        
+        public static void CheckUnsavedProgress(float currentGameTime)
+        {
+            // Om speltiden har ökat sedan senaste sparningen, markera som osparad
+            if (currentGameTime > LastSavedGameTime + 1.0f) // 1 sekund tolerans
+            {
+                HasUnsavedProgress = true;
+            }
+        }
+        
+        public static void ResetGameState()
+        {
+            LoadedGameTime = -1;
+            CurrentGameSeed = null;
+            LoadedInstance = null;
+            HasUnsavedProgress = false;
+            LastSavedGameTime = 0;
+        }
+    }
+}