test(timeline): add e2e journey + 375px axe for the layer filter

Playwright spec for /zeitstrahl: the primary journey (hide Letters → letter
cards vanish + trigger reports "1 aktiv" → reset restores) and a 375px axe pass
with the collapsible open in light and dark mode. Not skipped — #779 ships the
route. E2E is not wired into CI, so this runs locally only for now.

Refs #780
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/e2e/zeitstrahl-filter.spec.ts

@@ -0,0 +1,93 @@
+import AxeBuilder from '@axe-core/playwright';
+import { test, expect, type APIRequestContext } from '@playwright/test';
+
+/**
+ * Global /zeitstrahl layer filter (#780). Runs against the real stack with the
+ * seeded admin session (auth.setup). Covers the primary journey (hide the
+ * Letters layer → letter cards vanish + the trigger reports one active filter →
+ * reset restores everything) and a 375px axe pass with the collapsible open in
+ * both light and dark mode.
+ *
+ * #779 (the /zeitstrahl route) is merged, so this spec is NOT skipped. Per
+ * e2e/CLAUDE.md, E2E is not yet wired into CI — this axe gate runs locally only
+ * for now.
+ */
+
+const stamp = () => new Date().toISOString().replace(/[^0-9]/g, '');
+
+async function createPerson(request: APIRequestContext, firstName: string, lastName: string) {
+	const res = await request.post('/api/persons', {
+		data: { personType: 'PERSON', firstName, lastName }
+	});
+	if (!res.ok()) throw new Error(`create person failed: ${res.status()}`);
+	return (await res.json()).id as string;
+}
+
+/** Seeds one dated letter so the timeline has content (and a LetterCard to hide). */
+async function seedDatedLetter(request: APIRequestContext, isoDate: string, title: string) {
+	const senderId = await createPerson(request, 'Filter-Test', `Absender ${stamp()}`);
+	const receiverId = await createPerson(request, 'Filter-Test', `Empfaenger ${stamp()}`);
+
+	const createRes = await request.post('/api/documents', { multipart: { title } });
+	if (!createRes.ok()) throw new Error(`create document failed: ${createRes.status()}`);
+	const docId = (await createRes.json()).id as string;
+
+	const put = await request.put(`/api/documents/${docId}`, {
+		multipart: {
+			title,
+			documentDate: isoDate,
+			metaDatePrecision: 'DAY',
+			senderId,
+			receiverIds: receiverId
+		}
+	});
+	if (!put.ok()) throw new Error(`update document failed: ${put.status()}`);
+}
+
+test.describe('Zeitstrahl — layer filter (#780)', () => {
+	test('hiding the Letters layer removes letter cards and reports the active count; reset restores', async ({
+		page,
+		request
+	}) => {
+		// A sparse year keeps the seeded letter an individual card (not a dense strip).
+		const title = `E2E Filter Brief ${stamp()}`;
+		await seedDatedLetter(request, '1903-03-03', title);
+
+		await page.goto('/zeitstrahl');
+		await page.waitForSelector('[data-hydrated]');
+		await expect(page.getByText(title)).toBeVisible();
+
+		await page.getByTestId('timeline-filter-trigger').click();
+		await page.getByTestId('timeline-filter-letters').click();
+
+		await expect(page.getByText(title)).toHaveCount(0);
+		await expect(page.getByTestId('timeline-filter-trigger')).toContainText('1 aktiv');
+
+		await page.getByTestId('timeline-filter-reset').click();
+		await expect(page.getByText(title)).toBeVisible();
+	});
+
+	test('no wcag2a/wcag2aa violations at 375px with the filter bar open (light + dark)', async ({
+		page,
+		request
+	}) => {
+		await seedDatedLetter(request, '1915-06-15', `E2E Filter A11y ${stamp()}`);
+
+		await page.setViewportSize({ width: 375, height: 800 });
+		await page.goto('/zeitstrahl');
+		await page.waitForSelector('[data-hydrated]');
+
+		// Open the collapsible so axe scans the toggles, not just the trigger.
+		await page.getByTestId('timeline-filter-trigger').click();
+		await expect(page.getByTestId('timeline-filter-personal')).toBeVisible();
+
+		const scan = () => new AxeBuilder({ page }).withTags(['wcag2a', 'wcag2aa']).analyze();
+
+		const light = await scan();
+		expect(light.violations, JSON.stringify(light.violations, null, 2)).toEqual([]);
+
+		await page.evaluate(() => document.documentElement.setAttribute('data-theme', 'dark'));
+		const dark = await scan();
+		expect(dark.violations, JSON.stringify(dark.violations, null, 2)).toEqual([]);
+	});
+});