fix(view): ZOOM Extents fills the window at the real aspect (#364)

fit_to_bounds fitted the bounding box's circumscribed DIAGONAL into the
viewport height regardless of shape, so a wide drawing filled only a
small central patch. Fit against the actual viewport aspect instead —
required half-height = max(|y|, |x|/aspect) over the view-space corners
— and trim the border margin from 20% to 10%. ZOOM EXTENTS/ALL and
ZOOM WINDOW both pass the live pane aspect.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/scene/camera_ops.rs

@@ -107,7 +107,9 @@ impl Scene {
         if min == max {
             return;
         }
-        self.camera.borrow_mut().fit_to_bounds(min, max);
+        self.camera
+            .borrow_mut()
+            .fit_to_bounds(min, max, self.last_render_aspect.get().max(0.01));
         self.camera_generation += 1;
     }
 
@@ -850,7 +852,9 @@ impl Scene {
         if min == max {
             max += glam::Vec3::splat(1.0);
         }
-        self.camera.borrow_mut().fit_to_bounds(min, max);
+        self.camera
+            .borrow_mut()
+            .fit_to_bounds(min, max, self.last_render_aspect.get().max(0.01));
         self.camera_generation += 1;
     }