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

@@ -18,7 +18,7 @@
 
 <div class="h-full flex flex-col lg:flex-row pt-2 lg:pt-0 bg-gray-50 relative">
 	<button
-		class="absolute top-4 right-4 bg-yellow-500 text-white px-2 py-1 rounded-md shadow-md 
+		class="absolute top-4 right-4 bg-yellow-500 text-white px-2 py-1 rounded-md shadow-md
 		hover:bg-yellow-600 transition focus:outline-none text-sm lg:hidden"
 		onclick={toggleParticipants}
 	>
@@ -26,8 +26,8 @@
 	</button>
 
 	<div
-		class="group w-full max-w-md bg-white border rounded-lg shadow-md p-6 mx-4 my-2 h-fit text-base 
-		lg:text-lg transition-all duration-300 ease-in-out 
+		class="group w-full max-w-md bg-white border rounded-lg shadow-md p-6 mx-4 my-2 h-fit text-base
+		lg:text-lg transition-all duration-300 ease-in-out
 		hidden lg:block data-[open=true]:block"
 		data-open={showParticipants}
 	>