Hide sidebar collapse button on mobile

onItemClick is only passed on mobile, so use it to detect mobile context

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/app/share/[slug]/[[...path]]/ShareNav.tsx

@@ -162,11 +162,13 @@ export function ShareNav({
             </Row>
           </a>
         )}
+        {!onItemClick && (
           <Button variant="quiet" onPress={() => onCollapse?.(!collapsed)}>
             <Icon color="muted">
               <PanelLeft />
             </Icon>
           </Button>
+        )}
       </Row>
       {!collapsed && (
         <Column flexGrow={1} overflowY="auto">