Further cleanup, mostly with svelte 5 migration placeholder cleanup

frontend/src/lib/quiztivity/components/markdown/play.svelte

@@ -5,8 +5,6 @@ SPDX-License-Identifier: MPL-2.0
 -->
 
 <script lang="ts">
-	import { run } from 'svelte/legacy';
-
 	import type { Markdown } from '$lib/quiztivity/types';
 	import DOMPurify from 'dompurify';
 	import { marked } from 'marked';
@@ -18,11 +16,9 @@ SPDX-License-Identifier: MPL-2.0
 
 	let { data }: Props = $props();
 
-	let rendered_html = $state('');
-
-	run(() => {
-		rendered_html = browser ? DOMPurify.sanitize(marked.parse(data.markdown ?? '')) : '';
-	});
+	let rendered_html = $derived(
+		browser ? DOMPurify.sanitize(marked.parse(data.markdown ?? '')) : ''
+	);
 </script>
 
 <div class="prose dark:prose-invert">