test(auth): add no-nav-chrome regression test for signup page

Verifies signup page renders form and brand panel but no
navigation elements (tabs, sidebar, links to app routes).

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

frontend/src/routes/(public)/signup/page.test.ts

@@ -0,0 +1,33 @@
+import { describe, it, expect, vi } from 'vitest';
+import { render, screen } from '@testing-library/svelte';
+import Page from './+page.svelte';
+
+vi.mock('$app/stores', async () => {
+	const { readable } = await import('svelte/store');
+	return {
+		page: readable({ url: new URL('http://localhost/signup') })
+	};
+});
+
+describe('signup page', () => {
+	it('renders the signup form', () => {
+		render(Page);
+		expect(screen.getByText('Konto erstellen')).toBeInTheDocument();
+	});
+
+	it('renders the brand panel', () => {
+		render(Page);
+		expect(screen.getByText('Mealprep')).toBeInTheDocument();
+	});
+
+	it('does not render any navigation chrome', () => {
+		render(Page);
+		// No nav element should exist
+		expect(screen.queryByRole('navigation')).not.toBeInTheDocument();
+		// No app shell nav links
+		expect(screen.queryByText('Planer')).not.toBeInTheDocument();
+		expect(screen.queryByText('Rezepte')).not.toBeInTheDocument();
+		expect(screen.queryByText('Einkauf')).not.toBeInTheDocument();
+		expect(screen.queryByText('Einstellungen')).not.toBeInTheDocument();
+	});
+});