refactor(document-picker): downgrade listbox ARIA roles; fix unique listboxId

role=listbox + role=option without arrow-key navigation is misleading — the
WAI-ARIA combobox pattern requires aria-activedescendant handling that isn't
implemented. Downgraded to plain <ul>/<li>; input keeps role=combobox +
aria-controls pointing to the list id.

listboxId was a module-level constant so two simultaneous instances would share
the same DOM id. Fixed with a <script module> counter.

Updated spec queries from getByRole('option') to getByText() — tests behaviour,
not the ARIA implementation.

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

frontend/src/lib/document/DocumentPickerDropdown.svelte

@@ -1,3 +1,7 @@
+<script module>
+let _uid = 0;
+</script>
+
 <script lang="ts">
 import { m } from '$lib/paraglide/messages.js';
 import { clickOutside } from '$lib/shared/actions/clickOutside';
@@ -19,7 +23,7 @@ let {
 	onSelect
 }: Props = $props();
 
-const listboxId = 'doc-picker-listbox';
+const listboxId = `doc-picker-listbox-${++_uid}`;
 
 const picker = createDocumentTypeahead();
 
@@ -61,7 +65,6 @@ function handleSelect(doc: DocumentOption) {
 	{#if picker.isOpen && (picker.results.length > 0 || picker.loading)}
 		<ul
 			id={listboxId}
-			role="listbox"
 			class="ring-opacity-5 absolute z-50 mt-1 max-h-60 w-full overflow-auto rounded-md bg-surface py-1 text-sm shadow-lg ring-1 ring-black"
 		>
 			{#if picker.loading}
@@ -70,8 +73,6 @@ function handleSelect(doc: DocumentOption) {
 				{#each picker.results as doc (doc.id)}
 					{@const disabled = alreadyAddedIds.has(doc.id!)}
 					<li
-						role="option"
-						aria-selected={false}
 						aria-disabled={disabled}
 						onclick={() => handleSelect(doc)}
 						onkeydown={(e) => e.key === 'Enter' && handleSelect(doc)}