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/enrich/+page.server.ts

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