feat(bulk-upload): add UploadSaveBar component + fix bulk_save_cta message

Save bar with sticky positioning, a determinate progress bar while
uploading chunks, plural save CTA, and a destructive discard link.
Replaces broken ICU plural in bulk_save_cta with two-key approach
(bulk_save_cta_one / bulk_save_cta) since Paraglide 2.5 does not support
ICU plural syntax.

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

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

@@ -0,0 +1,48 @@
+import { describe, it, expect, vi, afterEach } from 'vitest';
+import { cleanup, render } from 'vitest-browser-svelte';
+import { page } from 'vitest/browser';
+import UploadSaveBar from './UploadSaveBar.svelte';
+
+afterEach(cleanup);
+
+describe('UploadSaveBar', () => {
+	it('shows plural label for multiple files', async () => {
+		render(UploadSaveBar, { fileCount: 5, onSave: vi.fn(), onDiscard: vi.fn() });
+		// "5 speichern →" or similar plural form
+		await expect.element(page.getByText(/5/)).toBeInTheDocument();
+	});
+
+	it('shows singular label for one file', async () => {
+		render(UploadSaveBar, { fileCount: 1, onSave: vi.fn(), onDiscard: vi.fn() });
+		// "Speichern →" singular form
+		await expect.element(page.getByText(/Speichern/i)).toBeInTheDocument();
+	});
+
+	it('progress bar is visible when chunkProgress is provided', async () => {
+		const { container } = render(UploadSaveBar, {
+			fileCount: 3,
+			chunkProgress: { done: 1, total: 3 },
+			onSave: vi.fn(),
+			onDiscard: vi.fn()
+		});
+		const progress = container.querySelector('progress');
+		expect(progress).not.toBeNull();
+		expect(progress?.getAttribute('value')).toBe('1');
+		expect(progress?.getAttribute('max')).toBe('3');
+	});
+
+	it('progress bar is not rendered when no chunkProgress', async () => {
+		const { container } = render(UploadSaveBar, {
+			fileCount: 2,
+			onSave: vi.fn(),
+			onDiscard: vi.fn()
+		});
+		const progress = container.querySelector('progress');
+		expect(progress).toBeNull();
+	});
+
+	it('discard link is rendered', async () => {
+		render(UploadSaveBar, { fileCount: 2, onSave: vi.fn(), onDiscard: vi.fn() });
+		await expect.element(page.getByText(/verwerfen/i)).toBeInTheDocument();
+	});
+});