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>