test(stammbaum): assert zoom-out floor via mirrored ?z; e2e affordance beforeEach (#692)

Strengthen the zoom-clamp test to assert z floors at 0.25 in the URL (was a
'does not throw' smoke test) and move the affordance localStorage reset to a
beforeEach so the e2e tests are order-independent (QA review).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/e2e/stammbaum-mobile.visual.spec.ts

@@ -17,10 +17,15 @@ test.describe('Stammbaum — mobile read path (#692)', () => {
 	// affordance appears; reduced-motion is already forced project-wide.
 	test.use({ hasTouch: true, isMobile: true });
 
+	// Clear the affordance-dismissed flag before every test so the first-load
+	// hint state is deterministic regardless of test order.
+	test.beforeEach(async ({ page }) => {
+		await page.addInitScript(() => localStorage.removeItem('stammbaumAffordanceDismissedAt'));
+	});
+
 	for (const width of WIDTHS) {
 		test(`affordance + controls render at ${width}px`, async ({ page }) => {
 			await page.setViewportSize({ width, height: 720 });
-			await page.addInitScript(() => localStorage.removeItem('stammbaumAffordanceDismissedAt'));
 			await page.goto('/stammbaum');
 			await expect(page.getByRole('heading', { name: 'Stammbaum' })).toBeVisible();
 

frontend/src/routes/stammbaum/page.svelte.test.ts

@@ -88,17 +88,22 @@ describe('stammbaum page', () => {
 		await expect.element(page.getByRole('complementary')).not.toBeInTheDocument();
 	});
 
-	it('clamps the zoom level when the zoom-out button is clicked many times', async () => {
+	it('clamps zoom-out at MIN_ZOOM (0.25), reflected in the mirrored ?z param', async () => {
 		mockPage.url = new URL('http://localhost/stammbaum');
+		replaceState.mockClear();
 		const Stammbaum = await loadComponent();
 		render(Stammbaum, {
 			props: { data: { nodes: sampleNodes, edges: [], initialView: DEFAULT_VIEW } }
 		});
 
 		const zoomOut = page.getByRole('button', { name: /verkleinern/i });
-		for (let i = 0; i < 10; i++) await zoomOut.click();
-		// Just verify that repeated clicks don't throw — branch coverage
-		await expect.element(zoomOut).toBeVisible();
+		// Default z=1; well over (1 - 0.25) / 0.1 = 8 steps to reach the floor.
+		for (let i = 0; i < 15; i++) await zoomOut.click();
+
+		await vi.waitFor(() => {
+			const url = replaceState.mock.calls.at(-1)![0] as URL;
+			expect(url.searchParams.get('z')).toBe('0.25');
+		});
 	});
 
 	it('mirrors the view into ?cx&cy&z when zoomed (US-PANEL-002 AC2)', async () => {