feat(ui): refine ribbon and view navigation

src/app/document.rs

@@ -209,6 +209,9 @@ pub(super) struct DocumentTab {
     /// device with no middle mouse button (a trackpad / web client). Exited
     /// with Esc or by starting another command.
     pub(super) pan_mode: bool,
+    /// Interactive 3-D orbit mode. While active, a left-button drag follows
+    /// the same camera-orbit path as Shift + middle-button drag.
+    pub(super) orbit_mode: bool,
     /// Per-plugin document state (`plugin::BuiltinPlugin` manifest id → state).
     #[cfg_attr(target_arch = "wasm32", allow(dead_code))]
     pub(super) plugin_state: HashMap<&'static str, Box<dyn Any + Send + Sync>>,
@@ -479,6 +482,7 @@ impl DocumentTab {
             thumbnail_cache_key: None,
             is_start: false,
             pan_mode: false,
+            orbit_mode: false,
             plugin_state: HashMap::new(),
             suspended_cmd: None,
         }