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/view/modal.rs

@@ -317,6 +317,7 @@ impl OpenCADStudio {
                             commandline_fade_ms: self.commandline_fade_ms,
                             zoom_wheel_reversed: self.zoom_wheel_reversed,
                             touchpad_pan: self.touchpad_pan,
+                            ui_scale_percent: self.ui_scale_percent,
                             zoom_factor: self.zoom_factor,
                             texteditmode: self.texteditmode,
                             dimension_continue_mode: self.dimension_continue_mode,