test(#118): add axe-core wcag2a/wcag2aa accessibility checks to E2E suite

Installs @axe-core/playwright and adds e2e/accessibility.spec.ts covering:
- home, persons, admin (authenticated via stored admin session)
- login (unauthenticated context)

Uses wcag2a + wcag2aa tags. Violations are logged with impact level and
node count before the assertion fails, so the first run against the live
stack will produce a clear inventory of any issues to fix or exclude.

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

frontend/e2e/accessibility.spec.ts

@@ -0,0 +1,58 @@
+import AxeBuilder from '@axe-core/playwright';
+import { test, expect } from '@playwright/test';
+
+/**
+ * Automated accessibility checks using axe-core (wcag2a + wcag2aa).
+ * Authenticated pages use the stored admin session from playwright.config.ts.
+ * The login page test overrides to an unauthenticated context.
+ *
+ * On first run: if violations are found they are logged with full details so
+ * that they can be either fixed or explicitly excluded here with a comment
+ * explaining the reason.
+ */
+
+const AUTHENTICATED_PAGES = [
+	{ name: 'home', path: '/' },
+	{ name: 'persons', path: '/persons' },
+	{ name: 'admin', path: '/admin' }
+];
+
+test.describe('Accessibility — authenticated pages', () => {
+	for (const { name, path } of AUTHENTICATED_PAGES) {
+		test(`${name} page has no critical wcag2a/wcag2aa violations`, async ({ page }) => {
+			await page.goto(path);
+			await page.waitForSelector('[data-hydrated]');
+
+			const results = await new AxeBuilder({ page }).withTags(['wcag2a', 'wcag2aa']).analyze();
+
+			if (results.violations.length > 0) {
+				const summary = results.violations
+					.map((v) => `[${v.impact}] ${v.id}: ${v.description} (${v.nodes.length} node(s))`)
+					.join('\n');
+				console.log(`\nAccessibility violations on ${name}:\n${summary}`);
+			}
+
+			expect(results.violations).toEqual([]);
+		});
+	}
+});
+
+test.describe('Accessibility — login page', () => {
+	test.use({ storageState: { cookies: [], origins: [] } });
+
+	test('login page has no critical wcag2a/wcag2aa violations', async ({ page }) => {
+		await page.goto('/login');
+		await expect(page.getByLabel('Benutzername')).toBeVisible();
+
+		const results = await new AxeBuilder({ page }).withTags(['wcag2a', 'wcag2aa']).analyze();
+
+		if (results.violations.length > 0) {
+			const summary = results.violations
+				.map((v) => `[${v.impact}] ${v.id}: ${v.description} (${v.nodes.length} node(s))`)
+				.join('\n');
+			console.log(`\nAccessibility violations on login:\n${summary}`);
+		}
+
+		expect(results.violations).toEqual([]);
+	});
+});