test(documents): add component tests for sender/receiver URL prefill on new document page

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/routes/documents/new/+page.svelte

@@ -3,14 +3,15 @@ import { enhance } from '$app/forms';
 import TagInput from '$lib/components/TagInput.svelte';
 import PersonTypeahead from '$lib/components/PersonTypeahead.svelte';
 import PersonMultiSelect from '$lib/components/PersonMultiSelect.svelte';
+import { untrack } from 'svelte';
 import { m } from '$lib/paraglide/messages.js';
 
 let { data, form } = $props();
 
 let tags: string[] = $state([]);
-let senderId = $state(data.initialSenderId);
+let senderId = $state(untrack(() => data.initialSenderId));
 let selectedReceivers: { id: string; firstName: string; lastName: string }[] = $state(
-	data.initialReceivers
+	untrack(() => data.initialReceivers)
 );
 
 let dateDisplay = $state('');