fix(bulk-upload): include tagNames in quick-upload metadata payload

Tags were silently dropped because the metadata object built in save()
never included a tagNames field; they never reached the backend.

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

frontend/src/lib/components/document/BulkDocumentEditLayout.svelte

@@ -100,7 +100,8 @@ async function save() {
 			titles: chunk.map((e) => e.title),
 			senderId: senderId || null,
 			receiverIds: selectedReceivers.map((r) => r.id),
-			documentDate: dateIso || null
+			documentDate: dateIso || null,
+			tagNames: tags.map((t) => t.name)
 		};
 		formData.append('metadata', new Blob([JSON.stringify(metadata)], { type: 'application/json' }));
 		const res = await fetch('/api/documents/quick-upload', { method: 'POST', body: formData });