feat(bulk-edit): add canWrite-gated row checkboxes on /documents and /enrich

Each row in the document search list and the enrichment queue gets a
WCAG-compliant (44px touch target) checkbox bound to bulkSelectionStore.
Checkbox click does not trigger the row's stretched-link navigation —
it sits inside the z-10 content sibling, the link is in the z-0 sibling,
so click events do not bubble between them.

Refs #225

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

frontend/src/lib/components/DocumentRow.svelte

@@ -4,13 +4,14 @@ import type { components } from '$lib/generated/api';
 import { applyOffsets } from '$lib/search';
 import { formatDate } from '$lib/utils/date';
 import * as m from '$lib/paraglide/messages.js';
+import { bulkSelectionStore } from '$lib/stores/bulkSelection.svelte';
 import ProgressRing from './ProgressRing.svelte';
 import ContributorStack from './ContributorStack.svelte';
 import DocumentThumbnail from './DocumentThumbnail.svelte';
 
 type DocumentSearchItem = components['schemas']['DocumentSearchItem'];
 
-let { item }: { item: DocumentSearchItem } = $props();
+let { item, canWrite = false }: { item: DocumentSearchItem; canWrite?: boolean } = $props();
 
 const doc = $derived(item.document);
 const titleText = $derived(doc.title || doc.originalFilename);
@@ -55,6 +56,21 @@ function safeTagColor(color: string | null | undefined): string {
 	<a href="/documents/{doc.id}" aria-label={titleText} class="absolute inset-0 z-0 block"></a>
 	<div class="pointer-events-none relative z-10 px-4 py-4 sm:py-5">
 		<div class="flex gap-3 sm:gap-5">
+			<!-- Bulk-selection checkbox -->
+			{#if canWrite}
+				<label
+					class="pointer-events-auto flex min-h-[44px] min-w-[44px] flex-shrink-0 cursor-pointer items-start pt-1"
+					data-testid="bulk-select-checkbox"
+				>
+					<input
+						type="checkbox"
+						class="h-5 w-5 cursor-pointer accent-brand-navy"
+						checked={bulkSelectionStore.has(doc.id)}
+						onchange={() => bulkSelectionStore.toggle(doc.id)}
+						aria-label={m.bulk_edit_select_document({ title: titleText })}
+					/>
+				</label>
+			{/if}
 			<!-- Thumbnail tile -->
 			<DocumentThumbnail doc={doc} size="lg" />