feat(bulk-edit): add BulkSelectionBar and Alle-X-editieren fast path

- BulkSelectionBar component: sticky bottom bar shown only when canWrite
  and selection is non-empty. Buttons meet WCAG 44px touch targets and
  iOS safe-area inset is honoured.
- Bar mounted on /documents and /enrich.
- Alle X editieren button on /documents replaces the selection with
  every UUID matching the active filter (via /api/documents/ids) and
  jumps to /documents/bulk-edit.

Refs #225

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

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

@@ -0,0 +1,49 @@
+import { afterEach, describe, expect, it, vi } from 'vitest';
+import { cleanup, render } from 'vitest-browser-svelte';
+import { page } from 'vitest/browser';
+import { goto } from '$app/navigation';
+import BulkSelectionBar from './BulkSelectionBar.svelte';
+import { bulkSelectionStore } from '$lib/stores/bulkSelection.svelte';
+
+vi.mock('$app/navigation', () => ({ goto: vi.fn() }));
+
+afterEach(() => {
+	cleanup();
+	vi.mocked(goto).mockClear();
+	bulkSelectionStore.clear();
+});
+
+describe('BulkSelectionBar', () => {
+	it('does not render when canWrite is false', async () => {
+		bulkSelectionStore.add('a');
+		render(BulkSelectionBar, { canWrite: false });
+		await expect.element(page.getByTestId('bulk-selection-bar')).not.toBeInTheDocument();
+	});
+
+	it('does not render when selection is empty', async () => {
+		render(BulkSelectionBar, { canWrite: true });
+		await expect.element(page.getByTestId('bulk-selection-bar')).not.toBeInTheDocument();
+	});
+
+	it('renders with the current selection count', async () => {
+		bulkSelectionStore.add('a');
+		bulkSelectionStore.add('b');
+		render(BulkSelectionBar, { canWrite: true });
+		await expect.element(page.getByTestId('bulk-selection-count')).toHaveTextContent('2');
+	});
+
+	it('clear button empties the store', async () => {
+		bulkSelectionStore.add('a');
+		bulkSelectionStore.add('b');
+		render(BulkSelectionBar, { canWrite: true });
+		await page.getByTestId('bulk-clear-all').click();
+		expect(bulkSelectionStore.size).toBe(0);
+	});
+
+	it('Massenbearbeitung navigates to /documents/bulk-edit', async () => {
+		bulkSelectionStore.add('a');
+		render(BulkSelectionBar, { canWrite: true });
+		await page.getByTestId('bulk-edit-open').click();
+		expect(vi.mocked(goto)).toHaveBeenCalledWith('/documents/bulk-edit');
+	});
+});