test(ui): add tests for 0 blocks and lastEditedAt on PanelHeader

Verifies blockCount=0 shows "0 Abschnitte" and that a provided
lastEditedAt value renders a formatted date containing the year.

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

frontend/src/lib/components/TranscriptionPanelHeader.svelte.test.ts

@@ -105,4 +105,32 @@ describe('TranscriptionPanelHeader', () => {
 
 		await expect.element(page.getByText('5 Abschnitte')).toBeInTheDocument();
 	});
+
+	it('should show "0 Abschnitte" when blockCount is 0', async () => {
+		render(TranscriptionPanelHeader, {
+			mode: 'edit',
+			hasBlocks: false,
+			blockCount: 0,
+			lastEditedAt: null,
+			onModeChange: () => {},
+			onClose: () => {}
+		});
+
+		await expect.element(page.getByText('0 Abschnitte')).toBeInTheDocument();
+	});
+
+	it('should show formatted date when lastEditedAt is provided', async () => {
+		render(TranscriptionPanelHeader, {
+			mode: 'read',
+			hasBlocks: true,
+			blockCount: 3,
+			lastEditedAt: '2026-04-07T10:00:00Z',
+			onModeChange: () => {},
+			onClose: () => {}
+		});
+
+		const statusText = document.querySelector('.hidden.md\\:block');
+		expect(statusText).not.toBeNull();
+		expect(statusText!.textContent).toContain('2026');
+	});
 });