refactor: normalize data directory naming, and consolidate serial connection handling

src/pygui/backend/data/local_settings_model.py

@@ -7,6 +7,7 @@ from typing import Any
 from PySide6.QtCore import QObject, Property, QDateTime, QStandardPaths, Signal, Slot
 
 from pygui.backend.data.local_settings import LocalSettings
+from pygui.backend.data.constants import DEFAULT_DATA_DIR_NAME
 
 
 MASTER_FAMILIES = ("A", "B", "C", "D", "E", "F", "P", "X", "Z")
@@ -52,7 +53,7 @@ class LocalSettingsModel(QObject):
             QStandardPaths.DocumentsLocation
         )
         base_dir = Path(documents_dir) if documents_dir else (Path.home() / "Documents")
-        return base_dir / "ISC_DATA"
+        return base_dir / DEFAULT_DATA_DIR_NAME
 
     def _new_defaults(self) -> dict[str, Any]:
         return {