-VIEW sEttings Background dialog and view backgrounds

Color, Gradient and Image at the background prompt open a Background
dialog (None / Solid / Gradient / Image, preview, solid colour, two- or
three-colour gradient with rotation, image file with position and
scale). Apply links the view to a new background object in
ACAD_BACKGROUND; restoring a view gives the model viewport a copy of
it (or none), and saving a view copies the viewport's background.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/app/update/mod.rs

@@ -8799,6 +8799,13 @@ impl OpenCADStudio {
                     self.close_sheet_set_dialog();
                     return Task::none();
                 }
+                // The Background dialog returns to -VIEW's settings prompt.
+                if self.active_modal == Some(super::ModalKind::ViewBackground) {
+                    self.view_background = None;
+                    self.close_active_modal();
+                    let i = self.active_tab;
+                    return self.run_dash_view("SETTINGS", i);
+                }
                 if self.active_modal == Some(super::ModalKind::Field) {
                     self.close_field_dialog();
                     return Task::none();