chore: clear compiler warnings

Remove accidental dead code (unused imports, the superseded paste tool()
helper, a never-read TORIENT handles field, a duplicate let binding, an
unneeded mut) and mark intentional-but-unwired scaffolding with
allow(dead_code): the web-only save_to_bytes, the plugin loadable() probe,
the planned PICK_HIGHLIGHT colours, the DynFieldSpec label, and the layout
ribbon helpers. Native build is now warning-clean apart from the upstream
nom/quick-xml future-incompat notices.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/commands.rs

@@ -1204,7 +1204,7 @@ impl OpenCADStudio {
                     let cam_rot = self.tabs[i].scene.camera.borrow().rotation;
                     let right = cam_rot * glam::Vec3::X;
                     let view_twist = right.y.atan2(right.x) as f64;
-                    let new_cmd = TorientCommand::new(handles, entities, view_twist);
+                    let new_cmd = TorientCommand::new(entities, view_twist);
                     self.command_line.push_info(&new_cmd.prompt());
                     self.tabs[i].active_cmd = Some(Box::new(new_cmd));
                 }