test(calendar-web): add E2E test for 404 error page

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/calendar/apps/web/e2e/error-page.spec.ts

@@ -0,0 +1,19 @@
+import { test, expect } from '@playwright/test';
+
+test.describe('Error Page', () => {
+	test('visiting a nonexistent route shows error page with status code', async ({ page }) => {
+		const response = await page.goto('/nonexistent-route-that-does-not-exist');
+
+		// SvelteKit should return a 404 status
+		expect(response?.status()).toBe(404);
+
+		// The error page should display the status code
+		const statusHeading = page.locator('h1');
+		await expect(statusHeading).toBeVisible({ timeout: 10000 });
+		await expect(statusHeading).toContainText('404');
+
+		// Should show a "back to home" link
+		const backLink = page.locator('a[href="/"]');
+		await expect(backLink).toBeVisible();
+	});
+});