fix: Restore touchstart handler for maximum reliability

frontend/src/app.rs

@@ -346,6 +346,7 @@ pub fn App() -> impl IntoView {
                         <div 
                             class="fixed inset-0 bg-black/60 backdrop-blur-sm transition-opacity cursor-default"
                             on:click=move |_| set_show_mobile_sidebar.set(false)
+                            on:touchstart=move |_| set_show_mobile_sidebar.set(false)
                         ></div>
                         <aside 
                             class={format!("relative w-80 max-w-[85vw] h-full shadow-2xl p-6 flex flex-col animate-in slide-in-from-left duration-300 border-r {}", sidebar_bg)}