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/command-center/command-center.tsx

@@ -592,6 +592,7 @@ export function CommandCenter() {
     return (
       <IsolatedBottomSheetModal
         ref={sheetRef}
+        contextBridge={null}
         snapPoints={COMMAND_CENTER_SNAP_POINTS}
         index={0}
         enableDynamicSizing={false}