Adopts the design language from Dammyjay93/interface-design: warm Stone neutrals, accent orange (#EA580C), borders-only depth (no shadows), 8px spacing grid, all-caps section labels, mono typography for machine names and timecodes.
Themes/StoneTheme.xaml is the single source of truth for design tokens (color brushes, typography styles, spacing) plus restyled control templates (Button, TextBox, ComboBox, ComboBoxItem, CheckBox, DataGrid + DataGridColumnHeader / DataGridRow / DataGridCell, ScrollBar). MainWindow consumes the tokens and is laid out with a header (title + status pill), section-headed Settings sidebar (Output Format / NDI Network / Display), card-wrapped participant list, and a mono status footer.
Settings sidebar surfaces the new NDI group configuration (discovery + output) and a Hide-(Local) checkbox. The latter filters the user's own self-preview from the participants list at the MainViewModel layer (HideLocalSelf=true by default) so operators don't accidentally route their own preview as an ISO. Apply Changes round-trips both FrameProcessingSettings and NdiGroupSettings through the controller in one go.
