fix(e2e): fix locale cookie httpOnly and add hydration waits

Paraglide's client-side setLocale writes the locale via document.cookie,
which silently fails for HttpOnly cookies. SvelteKit's cookies.set()
defaults to httpOnly: true, so locale switching never worked in tests.
Fix by setting httpOnly: false on the locale cookie (it's a UI preference,
not a credential — no security concern).

Add waitForSelector('[data-hydrated]') before any click that relies on
SvelteKit JavaScript event handlers. Without this, the click fires before
hydration and the onclick handler is not yet registered.

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

frontend/e2e/persons.spec.ts

@@ -87,6 +87,7 @@ test.describe('Conversations', () => {
 
 	test('sort toggle changes the button label', async ({ page }) => {
 		await page.goto('/conversations');
+		await page.waitForSelector('[data-hydrated]');
 		const btn = page.getByRole('button', { name: /Sortierung/i });
 		await expect(btn).toContainText('Neueste zuerst');
 		await btn.click();