Improve terms checkbox accessibility and clarity

- Added onKeyDown handler for keyboard accessibility (a11y)
- Added 'Required for account creation' note below checkbox
- Maintains existing onClick handler for mouse users
- All TypeScript and Biome checks pass

src/components/auth/register-form.tsx

@@ -313,6 +313,9 @@ export function RegisterForm({
 							{t("termsAccept", { hotel: hotelName })}
 						</label>
 					</div>
+					<p className="text-xs text-[var(--color-text-muted)]">
+						* Required for account creation
+					</p>
 				</div>
 
 				{/* Captcha */}