Underlays are rasterised for the view's scale; DGN V7 strokes one pixel wide

A page shown small was drawn from its full-size raster and thin lines broke
up into dots. Once a zoom settles on another quarter-octave step, PDF, DWF
and DGN underlays are rasterised again near their size on screen (never
above the full-size raster), frames are requested until that happens, and
the adjusted-pixel memo is kept per raster size. V7 element weights no longer
widen strokes, matching V8 models.

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

src/app/update/viewport.rs

@@ -850,6 +850,8 @@ impl OpenCADStudio {
         self.tabs[i].scene.update(t - self.start);
         // Dynamic dimensions keep their screen size across zoom bands.
         self.tabs[i].scene.refresh_dynamic_dimension_scales(false);
+        // Underlays are rasterised again for the zoom once it settles.
+        self.tabs[i].scene.refresh_underlay_resolution(t);
 
         // If the camera moved since we last synced, write it back to
         // the document and mark the file dirty.