fix: referral system — stop cabinet redirect to Telegram, fix deep link code handling

- Remove redirect to Telegram bot when email auth disabled + referral code present
  (cabinet links should stay on cabinet, bot links should go to bot)
- Remove referral_code from deep link auth (existing users can't get referrals)
- Don't consume referralCode in deep link path — leave it in localStorage for
  OIDC/widget auth methods that actually send it to the backend
- Consume campaign slug once into ref to survive retries (codesConsumedRef pattern)
- Update loginWithDeepLink to only accept (token, campaignSlug) — no referralCode
- Update pollDeepLinkToken API to match backend schema change

src/pages/Login.tsx

@@ -22,7 +22,7 @@ import LanguageSwitcher from '../components/LanguageSwitcher';
 import TelegramLoginButton from '../components/TelegramLoginButton';
 import OAuthProviderIcon from '../components/OAuthProviderIcon';
 import { saveOAuthState } from '../utils/oauth';
-import { consumeReferralCode, getPendingReferralCode } from '../utils/referral';
+import { getPendingReferralCode } from '../utils/referral';
 
 export default function Login() {
   const { t } = useTranslation();
@@ -146,16 +146,6 @@ export default function Login() {
     }
   };
 
-  const botUsername = import.meta.env.VITE_TELEGRAM_BOT_USERNAME || '';
-
-  // If email auth is disabled but user came with ref param, redirect to bot
-  useEffect(() => {
-    if (referralCode && emailAuthConfig?.enabled === false && botUsername) {
-      consumeReferralCode();
-      window.location.href = `https://t.me/${botUsername}?start=${encodeURIComponent(referralCode)}`;
-    }
-  }, [referralCode, emailAuthConfig, botUsername]);
-
   const appName = branding ? branding.name : import.meta.env.VITE_APP_NAME || 'VPN';
   const appLogo = branding?.logo_letter || import.meta.env.VITE_APP_LOGO || 'V';
   const logoUrl = branding ? brandingApi.getLogoUrl(branding) : null;