feat(commandline): float as bottom-centre overlay over the viewport

The command-line panel used to consume a full-width row at the bottom
of the main column, taking vertical space away from the drawing area
even when no command was active. Move it onto the viewport stack as a
fixed-width 720 px pill aligned to the bottom-centre, with rounded
corners so it reads as a floating element. The status bar still owns
the very bottom of the window.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/app/view.rs

@@ -504,10 +504,28 @@ impl OpenCADStudio {
             Space::new().into()
         };
 
-        let center_stack =
+        // Command-line sits as a bottom-centre overlay on top of the
-            iced::widget::stack![row![properties_el, viewport_stack].width(Fill).height(Fill),]
+        // viewport stack rather than as a separate row in the main
-                .width(Fill)
+        // column — frees up vertical space when no command is active
-                .height(Fill);
+        // and keeps the input close to where the cursor is drawing.
+        let command_line_overlay = iced::widget::container(self.command_line.view())
+            .width(Fill)
+            .height(Fill)
+            .align_x(iced::alignment::Horizontal::Center)
+            .align_y(iced::alignment::Vertical::Bottom)
+            .padding(iced::Padding {
+                top: 0.0,
+                right: 0.0,
+                bottom: 2.0,
+                left: 0.0,
+            });
+
+        let center_stack = iced::widget::stack![
+            row![properties_el, viewport_stack].width(Fill).height(Fill),
+            command_line_overlay,
+        ]
+        .width(Fill)
+        .height(Fill);
 
         let main_ui = container({
             let mut col = column![self.ribbon.view(
@@ -519,7 +537,6 @@ impl OpenCADStudio {
                 col = col.push(doc_tab_bar(&self.tabs, self.active_tab));
             }
             col.push(center_stack)
-                .push(self.command_line.view())
                 .push({
                     let is_model = tab.scene.current_layout == "Model";
                     let scale_pill_enabled = is_model

src/ui/command_line.rs

@@ -149,7 +149,7 @@ impl CommandLine {
                         a: 1.0,
                     },
                     width: 1.0,
-                    radius: 0.0.into(),
+                    radius: 2.0.into(),
                 },
                 icon: Color::WHITE,
                 placeholder: Color {
@@ -183,7 +183,7 @@ impl CommandLine {
                     border: Border {
                         color: BORDER_COLOR,
                         width: 1.0,
-                        radius: 0.0.into()
+                        radius: 3.0.into()
                     },
                     ..Default::default()
                 })
@@ -194,11 +194,11 @@ impl CommandLine {
             border: Border {
                 color: BORDER_COLOR,
                 width: 1.0,
-                radius: 0.0.into(),
+                radius: 4.0.into(),
             },
             ..Default::default()
         })
-        .width(Length::Fill)
+        .width(Length::Fixed(720.0))
         .into()
     }
 }