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

@@ -21,11 +21,12 @@
 		isShortScreen = typeof window !== 'undefined' && window.innerWidth < 1024;
 
 		function handleResize() {
-			const wasShortScreen = isShortScreen;
-			isShortScreen = window.innerWidth < 1024;
-
-			if (!isShortScreen && wasShortScreen) {
-				showParticipants = true;
+			const newShortScreen = window.innerWidth < 1024;
+			if (newShortScreen !== isShortScreen) {
+				isShortScreen = newShortScreen;
+				if (!isShortScreen) {
+					showParticipants = true; 
+				}
 			}
 		}
 
@@ -52,9 +53,7 @@
 
 	<div
 		class="bg-white border rounded-lg shadow-md p-6 mx-4 my-2 h-fit w-full max-w-md text-base lg:text-lg"
-		class:!hidden={typeof window !== 'undefined' &&
-			!showParticipants &&
-			!window.matchMedia('(min-width: 1024px)').matches}
+		class:hidden={isShortScreen && !showParticipants}
 	>
 		<h2 class="text-xl truncate font-semibold text-gray-700 text-center mb-4">
 			{$t('utils.words.participants')}