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/ui/window/options.rs

@@ -63,6 +63,8 @@ pub struct AppPrefs {
     pub hatch_associative: bool,
     /// ZOOMWHEEL: reverse the mouse-wheel zoom direction.
     pub zoom_wheel_reversed: bool,
+    /// Which mouse gestures pan and orbit the model view.
+    pub navigation_style: crate::app::settings::NavigationStyle,
     /// Scroll pans and Ctrl+scroll zooms (touchpads).
     pub touchpad_pan: bool,
     /// Interface scale in percent.
@@ -1274,6 +1276,16 @@ pub fn view_window<'a>(
         Space::new().height(10),
         spacemouse,
         Space::new().height(12),
+        text(crate::t!("Navigation style")).size(15),
+        Space::new().height(10),
+        iced::widget::pick_list(
+            Some(prefs.navigation_style),
+            crate::app::settings::NavigationStyle::ALL,
+            |style| style.to_string(),
+        )
+        .on_select(Message::NavigationStyleChanged)
+        .text_size(12),
+        Space::new().height(12),
         text(crate::t!("Zoom")).size(15),
         Space::new().height(10),
         row![