ENH: VPAW Visualize and `qt.QSettings`

The `VPAW Model` module was recently updated to store form field values via `qt.QSettings()` so that the form field values are application-wide, not scene-specific, and will be re-populated when the VPAW application is restarted. Consider doing the same for one or more form fields in the `VPAW Visualize` module. Also, for the form field(s) that are duplicated between the two modules (e.g., the data directory) consider whether they should be forced to be equal vs. stored and re-populated independently.

Start by comparing the VPAW Model module's existing qt.QSettings handling with the form fields in VPAW Visualize. Identify which Visualize fields should persist, review the duplicated fields such as the data directory, and clarify whether they should share or independently store values; done means the chosen fields are restored after restart with consistent duplicate-field behavior.

Written by the indexing model from the issue text.