add long-press gesture for touch-friendly preset popup

- replace instant drag-on-press with 500ms long-press timer
- cancel long-press on early release or movement past 10px threshold
- preserve double-click for mouse users (backward compatible)
- resize edge detection still instant (no long-press)
- cancel long-press on mouse_exit and grid rebuild
- fix: ConfigFile reserved word 'default' removed from config

autoload/layout_manager.gd

@@ -12,8 +12,8 @@ signal layout_loaded(layout_name: String)
 
 const LAYOUT_DIR: String = "res://config/layouts/"
 
-## Current layout name (e.g. "default").
-var current_layout_name: String = "default"
+## Current layout name (e.g. "Main").
+var current_layout_name: String = "Main"
 
 ## The active layout data: tile_id -> {col, row, w, h}
 var _layout: Dictionary = {}
@@ -28,7 +28,7 @@ func _ready() -> void:
 		current_layout_name = configured_name
 
 	if not load_layout(current_layout_name):
-		current_layout_name = "default"
+		current_layout_name = "Main"
 		_layout.clear()