Fix facility discovery in exported builds and verify first construction

scripts/core/definition_registry.gd

@@ -266,7 +266,9 @@ func _validate_requested_path(path: String) -> bool:
 			"Facility definitions must use the .tres extension."
 		)
 		valid = false
-	if not FileAccess.file_exists(path):
+	# Exported .tres resources are remapped to binary .res files. Physical
+	# FileAccess checks incorrectly reject them when no source checkout exists.
+	if not ResourceLoader.exists(path):
 		_add_error(
 			&"resource_not_found",
 			&"",