navigation: selectable mouse navigation style

Options → User Preferences → Navigation style picks which mouse
gestures pan and orbit the model view (#1480):

- CAD (default): middle button pans, Shift + middle button orbits.
- Blender: middle button orbits, Shift + middle button pans.
- CATIA: middle button pans; pressing the left button during it orbits,
  so 3D navigation needs only the mouse.

An armed orbit tool always orbits. The choice is saved with the user
settings.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/app/view/modal.rs

@@ -312,6 +312,7 @@ impl OpenCADStudio {
                             show_ribbon: !self.ribbon_closed,
                             hatch_associative: self.hatch_associative,
                             zoom_wheel_reversed: self.zoom_wheel_reversed,
+                            navigation_style: self.navigation_style,
                             touchpad_pan: self.touchpad_pan,
                             ui_scale_percent: self.ui_scale_percent,
                             zoom_factor: self.zoom_factor,