test: cover DocumentThumbnail, UnsavedWarningBanner, PersonsStatsBar

DocumentThumbnail: thumbnailUrl→img branch, no-thumbnail→placeholder
icon branch, sm vs lg size container class, lazy/async loading attrs.

UnsavedWarningBanner: warning text, discard button, callback wiring.

PersonsStatsBar: count rendering, singular/plural label switching for
both persons and documents (4 branches), zero-count plural fallback.

14 tests across three small primitive files.

Refs #496.

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

frontend/src/lib/shared/primitives/UnsavedWarningBanner.svelte.test.ts

@@ -0,0 +1,29 @@
+import { describe, it, expect, vi, afterEach } from 'vitest';
+import { cleanup, render } from 'vitest-browser-svelte';
+import { page } from 'vitest/browser';
+import UnsavedWarningBanner from './UnsavedWarningBanner.svelte';
+
+afterEach(cleanup);
+
+describe('UnsavedWarningBanner', () => {
+	it('renders the warning text', async () => {
+		render(UnsavedWarningBanner, { props: { onDiscard: () => {} } });
+
+		await expect.element(page.getByText(/ungespeicherte änderungen/i)).toBeVisible();
+	});
+
+	it('renders the discard action button', async () => {
+		render(UnsavedWarningBanner, { props: { onDiscard: () => {} } });
+
+		await expect.element(page.getByRole('button', { name: /verwerfen/i })).toBeVisible();
+	});
+
+	it('calls onDiscard when the discard button is clicked', async () => {
+		const onDiscard = vi.fn();
+		render(UnsavedWarningBanner, { props: { onDiscard } });
+
+		await page.getByRole('button', { name: /verwerfen/i }).click();
+
+		expect(onDiscard).toHaveBeenCalledOnce();
+	});
+});