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/file.rs

@@ -663,6 +663,7 @@ impl OpenCADStudio {
             polar_increment_deg: self.polar_increment_deg,
             zoom_wheel_reversed: self.zoom_wheel_reversed,
             touchpad_pan: self.touchpad_pan,
+            ui_scale_percent: self.ui_scale_percent,
             zoom_factor: self.zoom_factor,
             cursor_size: self.cursor_size,
             pick_box: self.pick_box,
@@ -764,6 +765,7 @@ impl OpenCADStudio {
         self.polar_increment_deg = s.polar_increment_deg;
         self.zoom_wheel_reversed = s.zoom_wheel_reversed;
         self.touchpad_pan = s.touchpad_pan;
+        self.ui_scale_percent = crate::app::settings::clamp_ui_scale(s.ui_scale_percent);
         self.zoom_factor = crate::app::settings::clamp_zoom_factor(s.zoom_factor);
         // Like the drafting-rotation field below, the Options field edits a
         // buffer rather than the value, so it is reseeded whenever the value

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