Fix/121 user list responsiveness

This MR addresses the issue where the user list wasn't responsive on smaller screens (look at the user list within a chat session):

• Toggle button is only displayed on short screen to display the user list
• the user list is now adapted for different screen sizes

Remark: There are other pages/components in the app that are not fully responsive yet.

frontend/src/routes/sessions/[id]/+page.svelte

@@ -22,7 +22,7 @@
 		isShortScreen.set(window.innerWidth < 1024);
 	}
 	window.addEventListener('resize', handleResize);
-	handleResize(); 
+	handleResize();
 </script>
 
 <div class="h-full flex lg:flex-row flex-col pt-2 lg:pt-0 bg-gray-50 relative">