feat(options): interface scale for the whole window

On a non-Retina screen macOS draws the interface at 1x, which reads small
on a Full HD monitor, and there was no way to enlarge it. Options >
Display now offers an interface scale of 75–200 % in 25 % steps, applied
through the window's scale factor on top of the display's own and kept
with the user settings. It is a list rather than a slider because the
dialog rescales under the pointer as the value changes.

Fixes #1655

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/app/update/mod.rs

@@ -8391,6 +8391,12 @@ impl OpenCADStudio {
                 Task::none()
             }
 
+            Message::UiScaleChanged(percent) => {
+                self.ui_scale_percent = crate::app::settings::clamp_ui_scale(percent);
+                self.persist_settings_if_changed();
+                Task::none()
+            }
+
             Message::ZoomFactorChanged(factor) => {
                 self.zoom_factor = crate::app::settings::clamp_zoom_factor(factor);
                 // The field beside the slider reads the same value, so the