Regenerate viewport dimensions when the viewport view changes

Panning, zooming, twisting or rescaling a layout viewport moves model
geometry across the sheet without touching that geometry, so nothing in
the ordinary entity-change path noticed and the dimensions drawn through
the viewport stayed where they were — detached from what they measure.

`Scene::notify_viewport_changed` announces the viewport itself as a
modified entity. That is all it takes: every trans-space reference
carries the viewport handle as the first link of its chain, so the
dependency lookup in `refresh_associative_dimensions` already finds the
associations from there, and the refresh re-places and re-measures them.

Called from each mutator that changes the paper<->model mapping: pan,
zoom, fit-to-bounds, view normalisation on entering MSPACE, the
view-direction/twist snaps, the viewcube camera path, and both
annotation-scale setters.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

src/scene/mod.rs

@@ -5296,6 +5296,10 @@ impl Scene {
         self.document
             .set_viewport_annotation_scale(viewport, scale_handle);
 
+        // Viewport scale changed: the dimensions drawn on the sheet
+        // through it measure the same model geometry at a new paper
+        // size and have to be re-placed.
+        self.notify_viewport_changed(viewport);
         self.resident_wire_sets.borrow_mut().clear();
         self.bump_geometry();
 
@@ -5349,6 +5353,10 @@ impl Scene {
         vp.view_height = vp.height / factor;
         self.document
             .set_viewport_annotation_scale(viewport, scale_handle);
+        // Viewport scale changed: the dimensions drawn on the sheet
+        // through it measure the same model geometry at a new paper
+        // size and have to be re-placed.
+        self.notify_viewport_changed(viewport);
         self.resident_wire_sets.borrow_mut().clear();
         self.bump_geometry();
         true