fix(view): correct 3D mesh interaction

Sync projection controls from the active camera, preserve the UCS icon in perspective views, and use visible or selected 3D geometry for orbit pivots. Dense mesh vertex grips remain hidden.

src/scene/mspace.rs

@@ -446,6 +446,15 @@ impl Scene {
         self.camera.borrow().rotation
     }
 
+    pub fn active_camera_projection(&self) -> view::camera::Projection {
+        if let Some(handle) = self.active_viewport {
+            if let Some(camera) = self.camera_for_viewport(handle) {
+                return camera.projection;
+            }
+        }
+        self.camera.borrow().projection
+    }
+
     /// View-rotation matrix for the active viewport (MSPACE), or the
     /// paper-space camera's matrix when not in MSPACE.
     /// Used by ViewCube hit-testing so clicks map to the correct camera.