feat(bulk-upload): add BulkDocumentEditLayout component with save handler

State-owner for the bulk upload flow:
- N=0: full-panel BulkDropZone
- N=1: title + shared metadata (no switcher/scope cards)
- N≥2: FileSwitcherStrip + per-file ScopeCard + shared ScopeCard
Save handler chunks files at 10/request, POSTs to /api/documents/quick-upload
with typed metadata JSON part, tracks progress, redirects to /documents.

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

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

@@ -0,0 +1,99 @@
+import { describe, it, expect, vi, afterEach } from 'vitest';
+import { cleanup, render } from 'vitest-browser-svelte';
+import { page, userEvent } from 'vitest/browser';
+import BulkDocumentEditLayout from './BulkDocumentEditLayout.svelte';
+
+afterEach(() => {
+	cleanup();
+	vi.unstubAllGlobals();
+});
+
+function makeFile(name: string): File {
+	return new File(['content'], name, { type: 'application/pdf' });
+}
+
+async function addFilesViaInput(container: HTMLElement, files: File[]): Promise<void> {
+	const input = container.querySelector('input[type="file"]') as HTMLInputElement;
+	if (!input) throw new Error('No file input found — is BulkDropZone visible?');
+	await userEvent.upload(input, files);
+}
+
+describe('BulkDocumentEditLayout', () => {
+	it('N=0: shows BulkDropZone', async () => {
+		render(BulkDocumentEditLayout, {});
+		await expect.element(page.getByTestId('bulk-drop-zone')).toBeInTheDocument();
+	});
+
+	it('N=1: file-switcher-strip and per-file scope card are absent', async () => {
+		const { container } = render(BulkDocumentEditLayout, {});
+		await addFilesViaInput(container, [makeFile('doc.pdf')]);
+		expect(container.querySelector('[data-testid="file-switcher-strip"]')).toBeNull();
+		expect(container.querySelector('[data-variant="per-file"]')).toBeNull();
+	});
+
+	it('N=5: file-switcher-strip and per-file scope card are both present', async () => {
+		const { container } = render(BulkDocumentEditLayout, {});
+		await addFilesViaInput(container, [
+			makeFile('a.pdf'),
+			makeFile('b.pdf'),
+			makeFile('c.pdf'),
+			makeFile('d.pdf'),
+			makeFile('e.pdf')
+		]);
+		expect(container.querySelector('[data-testid="file-switcher-strip"]')).not.toBeNull();
+		expect(container.querySelector('[data-variant="per-file"]')).not.toBeNull();
+	});
+
+	it('removing middle file preserves order of remaining files', async () => {
+		const { container } = render(BulkDocumentEditLayout, {});
+		await addFilesViaInput(container, [
+			makeFile('file0.pdf'),
+			makeFile('file1.pdf'),
+			makeFile('file2.pdf')
+		]);
+
+		// Remove the chip for file1 via its "Entfernen" remove button (second × button)
+		const removeButtons = container.querySelectorAll<HTMLButtonElement>(
+			'[data-testid="file-switcher-strip"] button[aria-label="Entfernen"]'
+		);
+		expect(removeButtons.length).toBe(3);
+		removeButtons[1].click(); // remove file1
+
+		// Wait for Svelte to flush the DOM update
+		await vi.waitFor(
+			() => {
+				const chips = container.querySelectorAll(
+					'[data-testid="file-switcher-strip"] [data-chip-id]'
+				);
+				expect(chips.length).toBe(2);
+				expect(chips[0].textContent?.trim()).toContain('file0');
+				expect(chips[1].textContent?.trim()).toContain('file2');
+			},
+			{ timeout: 1000 }
+		);
+	});
+
+	it('save calls fetch twice for 12 files (2 chunks of 10)', async () => {
+		const mockFetch = vi.fn().mockResolvedValue({
+			ok: true,
+			json: async () => ({ created: [], updated: [], errors: [] })
+		});
+		vi.stubGlobal('fetch', mockFetch);
+
+		// Also stub goto to prevent navigation errors in test
+		vi.mock('$app/navigation', () => ({ goto: vi.fn() }));
+
+		const { container } = render(BulkDocumentEditLayout, {});
+		const files = Array.from({ length: 12 }, (_, i) => makeFile(`f${i}.pdf`));
+		await addFilesViaInput(container, files);
+
+		const saveBtn = container.querySelector(
+			'button[data-testid="bulk-save-btn"]'
+		) as HTMLButtonElement;
+		expect(saveBtn).not.toBeNull();
+		saveBtn.click();
+
+		// Wait for async save to complete
+		await vi.waitFor(() => expect(mockFetch).toHaveBeenCalledTimes(2), { timeout: 3000 });
+	});
+});