feat: embed tile height placeholder inside arena .tscn files and bake terrain transform shifts natively instead of using code hacks

scenes/main.gd

@@ -166,13 +166,17 @@ func _instantiate_3d_arena(scene_path: String):
 			var arena_instance = arena_scene.instantiate()
 			arena_instance.name = "ArenaEnvironment3D"
 			
-			if "freemode" in scene_path or "stop_n_go" in scene_path:
-				# The Terrainv2.gltf (and related arenas) have their floor physically modeled around Y=0.22.
-				# Shift it down so the visual floor aligns properly with gridmap items.
-				arena_instance.position.y = -0.22
+			# Note: We no longer shift the arena via code (e.g., position.y = -0.22)
+			# The physical shifts have been baked directly into the .tscn files using EditorTileReference.
 				
 			add_child(arena_instance)
 			move_child(arena_instance, 0)
+			
+			# Clean up the EditorTileReference if it was left in the scene
+			var editor_ref = arena_instance.get_node_or_null("EditorTileReference")
+			if editor_ref:
+				editor_ref.queue_free()
+				
 			print("Instantiated 3D Arena: ", scene_path)
 
 func _hide_ground_tiles():
@@ -194,21 +198,16 @@ func _setup_effect_elevation():
 	if em and em.mesh_library:
 		var ml = em.mesh_library.duplicate()
 		
-		# Only lift tiles for modes that use the shifted Terrainv2.gltf (-0.22 offset)
+		# Now that terrain heights are perfectly aligned inside the .tscn files,
+		# we no longer need to dynamically lift all tiles by 0.08.
+		# However, we still need to slightly drop TILE_SAFE (id 2) so it 
+		# renders strictly as a floor decal without clipping.
 		if LobbyManager.game_mode in ["Stop n Go", "Freemode"]:
-			var lift_transform = Transform3D().translated(Vector3(0, 0.08, 0))
-			for id in ml.get_item_list():
-				if id == 4: continue # Skip hidden non-walkable blocks
-				
-				var apply_transform = lift_transform
-				# TILE_SAFE (2) is painted on Layer 2 (Y=0.10). 
-				# We want it below all grid tiles (Layer 0 is at 0.08) but above the terrain (0.06).
-				# We set it to 0.07 by applying a -0.03 offset (0.10 - 0.03 = 0.07).
-				if id == 2:
-					apply_transform = Transform3D().translated(Vector3(0, -0.03, 0))
-					
+			if ml.find_item_by_name("safe_zone") != -1 or 2 in ml.get_item_list():
+				var id = 2
 				var current_transform = ml.get_item_mesh_transform(id)
-				ml.set_item_mesh_transform(id, apply_transform * current_transform)
+				# Push it down by -0.02 so it sits perfectly between terrain and tiles
+				ml.set_item_mesh_transform(id, Transform3D().translated(Vector3(0, -0.02, 0)) * current_transform)
 		
 		em.mesh_library = ml