Dynamic dimensions: constant screen size, transform keeps the second constraint point

Every dynamic dimension gets a DIMSCALE override for 12 px text, refreshed
per zoom band, at creation and after load. A SCALE/ROTATE of an entity whose
own end points a driving dimension measures now pins its second constraint
point so the dimension moves the first end, as the reference does.

Co-Authored-By: Claude Fable 5.1 <[email protected]>

src/app/command_driver.rs

@@ -3688,6 +3688,7 @@ impl OpenCADStudio {
                 );
                 // DYNCONSTRAINTDISPLAY 0 also keeps a new dynamic dimension off screen.
                 self.tabs[i].scene.refresh_hidden_dynamic_dimensions();
+                self.tabs[i].scene.refresh_dynamic_dimension_scales(true);
                 self.tabs[i].dirty = true;
                 self.tabs[i].active_cmd = None;
                 self.tabs[i].snap_result = None;

src/app/update/viewport.rs

@@ -785,6 +785,8 @@ impl OpenCADStudio {
     pub(super) fn on_tick(&mut self, t: Instant) -> Task<Message> {
         let i = self.active_tab;
         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);
 
         // If the camera moved since we last synced, write it back to
         // the document and mark the file dirty.