fix(mobile): scroll #main-app instead of body on mobile

body/html have overflow:hidden so scrollTop is a no-op on them.
#main-app is the actual scroll container; use overflow-y:auto on
mobile and target it directly in scrollToNote and the scroll listener.

src/App.vue

@@ -28,7 +28,7 @@ const { isATProtoReady } = useATProtoLogin()
 
 @media screen and (max-width: 768px) {
   #main-app {
-    overflow: visible;
+    overflow-y: auto;
   }
 }