WinForms user settings lived in user.config under %LOCALAPPDATA%\OpenNest,
the Velopack install folder that setup clears on a reinstall, and the
default provider starts empty at each assembly version. Store them in
%APPDATA%\OpenNest\user-settings.json instead, carrying over any values
the old user.config still holds on first run.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
