fix(e2e): wait for hydration before clicking nav dropdown in logout test

waitForURL('/') resolves as soon as the URL changes but before SvelteKit
finishes hydrating — the avatar button's onclick is not yet registered,
so the click has no effect and the dropdown never opens.

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

frontend/e2e/auth.spec.ts

@@ -61,6 +61,9 @@ test.describe('Authentication', () => {
 
 	test('logout clears the session and redirects to /login', async ({ page }) => {
 		await login(page);
+		// Wait for hydration before interacting with the nav — onclick handlers are
+		// only wired up after SvelteKit finishes hydrating the page client-side.
+		await page.waitForSelector('[data-hydrated]');
 		// Logout is inside the user avatar dropdown — open it first.
 		// Wait for the dropdown button to be visible before clicking Abmelden,
 		// since the {#if userMenuOpen} block renders asynchronously in Svelte.