test(ui): cover the invitation-card single-word indicator

Make the mock invitation a Russian single-word game so the card's
"One word per turn" line renders, and assert it in the lobby e2e.

ui/e2e/social.spec.ts

@@ -48,6 +48,7 @@ test('invitations: the lobby shows an invitation and accepting clears it', async
   await loginLobby(page);
   await expect(page.getByText('Invitations')).toBeVisible();
   await expect(page.getByText(/From Kaya/)).toBeVisible();
+  await expect(page.getByText('One word per turn')).toBeVisible(); // the single-word-rule line on the card
   await page.getByRole('button', { name: /^Accept$/ }).click();
   await expect(page.getByText(/From Kaya/)).toBeHidden();
 });