update to svelte 5

src/lib/components/AvatarComponent.svelte

@@ -1,11 +1,13 @@
 <script lang="ts">
   import type { Account } from '$lib/mastodon/response';
 
-  export let account: Account;
-  let avatarDescription: string;
-  let sourceSetHtml: string;
-  $: avatarDescription = `Avatar for ${account.acct}`;
-  $: {
+  interface Props {
+    account: Account;
+  }
+
+  let { account }: Props = $props();
+  let avatarDescription: string = $derived(`Avatar for ${account.acct}`);
+  let sourceSetHtml: string = $derived.by(() => {
     // Sort thumbnails by file type. This is important, because the order of the srcset entries matter.
     // We need the best format to be first
     const formatPriority = new Map<string, number>([
@@ -33,8 +35,8 @@
       const srcset = entry[1].join(', ');
       html += `<source srcset="${srcset}" type="${entry[0]}" />`;
     }
-    sourceSetHtml = html;
-  }
+    return html;
+  });
 </script>
 
 <picture>