Remove outdated dungeon integration tests documentation and introduce new dungeon object system documentation

- Deleted the `dungeon-integration-tests.md` file, which contained comprehensive integration tests for the dungeon object rendering system.
- Added `dungeon-object-system.md`, detailing the architecture, object types, placement processes, rendering pipeline, and user interface components of the YAZE Dungeon Object System.
- Enhanced the DungeonEditor and DungeonObjectSelector with improved UI methods and object selection callbacks for better user interaction and object management.

src/app/editor/dungeon/dungeon_editor.h

@@ -89,6 +89,10 @@ class DungeonEditor : public Editor {
   void DrawDungeonTabView();
   void DrawDungeonCanvas(int room_id);
   
+  // Enhanced UI methods
+  void DrawCanvasAndPropertiesPanel();
+  void DrawRoomPropertiesDebugPopup();
+  
   // Room selection management
   void OnRoomSelected(int room_id);