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 });

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

@@ -116,6 +116,30 @@ describe('BulkDocumentEditLayout', () => {
 		await vi.waitFor(() => expect(mockFetch).toHaveBeenCalledTimes(1), { timeout: 3000 });
 	});
 
+	it('save() includes tagNames in metadata payload', async () => {
+		let capturedFormData: FormData | undefined;
+		const mockFetch = vi.fn().mockImplementation(async (_url: string, init: RequestInit) => {
+			capturedFormData = init?.body as FormData;
+			return { ok: true, json: async () => ({ created: [], updated: [], errors: [] }) };
+		});
+		vi.stubGlobal('fetch', mockFetch);
+
+		const { container } = render(BulkDocumentEditLayout, {});
+		await addFilesViaInput(container, [makeFile('doc.pdf')]);
+
+		const saveBtn = container.querySelector(
+			'button[data-testid="bulk-save-btn"]'
+		) as HTMLButtonElement;
+		saveBtn.click();
+
+		await vi.waitFor(() => expect(mockFetch).toHaveBeenCalledTimes(1), { timeout: 3000 });
+
+		expect(capturedFormData).toBeDefined();
+		const metadataBlob = capturedFormData!.get('metadata') as Blob;
+		const metadataJson = JSON.parse(await metadataBlob.text());
+		expect(metadataJson).toHaveProperty('tagNames');
+	});
+
 	it('discard-all resets to N=0 state and shows drop zone', async () => {
 		const { container } = render(BulkDocumentEditLayout, {});
 		await addFilesViaInput(container, [makeFile('a.pdf'), makeFile('b.pdf')]);