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/routes/DocumentList.svelte

@@ -119,7 +119,7 @@ function groupByReceiver(docItems: DocumentSearchItem[]) {
 			</div>
 			<ul class="divide-y divide-line">
 				{#each group.items as item (group.label + '-' + item.document.id)}
-					<DocumentRow item={item} />
+					<DocumentRow item={item} canWrite={canWrite} />
 				{/each}
 			</ul>
 		</div>

frontend/src/routes/enrich/+page.server.ts

@@ -19,5 +19,5 @@ export async function load({
 
 	const documents = result.response.ok ? (result.data ?? []) : [];
 
-	return { documents };
+	return { documents, canWrite };
 }

frontend/src/routes/enrich/+page.svelte

@@ -1,11 +1,13 @@
 <script lang="ts">
 import { m } from '$lib/paraglide/messages.js';
 import BackButton from '$lib/components/BackButton.svelte';
+import { bulkSelectionStore } from '$lib/stores/bulkSelection.svelte';
 
 let { data } = $props();
 
 const documents = $derived(data.documents);
 const count = $derived(documents.length);
+const canWrite = $derived(data.canWrite);
 </script>
 
 <div class="mx-auto max-w-4xl px-4 py-10">
@@ -61,8 +63,24 @@ const count = $derived(documents.length);
 		<div class="border border-line bg-surface shadow-sm">
 			<ul class="divide-y divide-line-2">
 				{#each documents as doc (doc.id)}
-					<li class="group transition-colors duration-200 hover:bg-muted">
-						<a href="/enrich/{doc.id}" class="flex items-center justify-between p-6">
+					<li class="group relative transition-colors duration-200 hover:bg-muted">
+						<a href="/enrich/{doc.id}" class="absolute inset-0 z-0 block" aria-label={doc.title}
+						></a>
+						<div class="pointer-events-none relative z-10 flex items-center justify-between p-6">
+							{#if canWrite}
+								<label
+									class="pointer-events-auto mr-4 flex min-h-[44px] min-w-[44px] flex-shrink-0 cursor-pointer items-center"
+									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: doc.title })}
+									/>
+								</label>
+							{/if}
 							<div class="min-w-0 flex-1">
 								<p class="font-serif text-lg font-medium text-ink group-hover:underline">
 									{doc.title}
@@ -74,7 +92,7 @@ const count = $derived(documents.length);
 								aria-hidden="true"
 								class="ml-4 h-5 w-5 shrink-0 opacity-30 transition-opacity group-hover:opacity-70"
 							/>
-						</a>
+						</div>
 					</li>
 				{/each}
 			</ul>