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/Modding/API/IModAPI.cs

@@ -0,0 +1,9 @@
+// Placeholder för mod API
+// Detta kommer att definiera interface för mod-utveckling
+
+namespace TheGame.Modding.API
+{
+    // TODO: Implementera IMod interface
+    // TODO: Implementera ModAPI class
+    // TODO: Definiera mod lifecycle events
+}

scripts/Modding/API/IModAPI.cs.uid

@@ -0,0 +1 @@
+uid://bpq0jeupss8q6