-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 <noreply@anthropic.com>

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();

src/app/update/style.rs

@@ -1162,6 +1162,18 @@ impl OpenCADStudio {
                     crate::ui::window::gradient_editor::GradientMsg::Color(index, color),
                 )))
             }
+            Some(crate::app::ColorPickTarget::ViewBackground(slot)) => {
+                let rgb = match color {
+                    codec::types::Color::Rgb { r, g, b } => Some([r, g, b]),
+                    codec::types::Color::Index(index) => {
+                        codec::types::aci_table::aci_to_rgb(index).map(|(r, g, b)| [r, g, b])
+                    }
+                    _ => None,
+                };
+                rgb.map(|rgb| {
+                    Message::PdfDialog(crate::ui::window::pdf_dialogs::PdfDialogMsg::BgColor(slot, rgb))
+                })
+            }
             Some(crate::app::ColorPickTarget::GraphicAttributesLine) => Some(
                 Message::GraphicAttributes(GraphicAttributesMsg::LineColor(color)),
             ),