fix(app): polish workspace navigation surfaces

Use mobile action sheets and long-press file menus while preserving provider context across sheet portals. Keep sidebar and file-pane glyphs on shared visual rails, avoid scrollbar layout shifts, and hide keyboard affordances where shortcuts are unavailable.

packages/app/src/components/ui/combobox.tsx

@@ -994,6 +994,7 @@ function MobileComboboxBody(props: MobileBodyProps): ReactElement {
   return (
     <IsolatedBottomSheetModal
       ref={props.bottomSheetRef}
+      contextBridge={null}
       snapPoints={props.snapPoints}
       index={0}
       enableDynamicSizing={false}