fix(view): keep named views of earlier versions at their place, in f64

A VIEW record's centre is an offset from its target in view coordinates.
Views saved by earlier versions stored the target itself as the centre;
treating that as an offset put them (and VIEW plots) at about twice the
coordinates. One shared `named_view_center` now resolves the centre in
f64 (DVec3/DQuat), taking a centre equal to a non-zero target as the old
convention; VIEW RESTORE, the view plot window and Place on Sheet use it.

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

src/app/update/file.rs

@@ -5519,8 +5519,8 @@ impl OpenCADStudio {
         let half_w = view.width.abs() * 0.5;
         let half_h = view.height.abs() * 0.5;
         (half_w > 1e-9 && half_h > 1e-9).then_some(())?;
-        // The view centre is relative to its target (plan views).
-        let (cx, cy) = (view.target.x + view.center.x, view.target.y + view.center.y);
+        let center = crate::scene::named_view_center(view);
+        let (cx, cy) = (center.x, center.y);
         self.area_plot_job((cx - half_w, cy - half_h, cx + half_w, cy + half_h))
     }