feat: TelegramLoginButton with OIDC popup + legacy widget fallback

- Add oidc_enabled/oidc_client_id to TelegramWidgetConfig interface and fallback
- Add loginTelegramOIDC API method for id_token auth
- Add loginWithTelegramOIDC to auth store
- Rewrite TelegramLoginButton: OIDC popup when enabled, legacy widget otherwise
- Extend Window.Telegram type with Login SDK in vite-env.d.ts

src/api/auth.ts

@@ -49,6 +49,20 @@ export const authApi = {
     return response.data;
   },
 
+  // Telegram OIDC authentication (popup flow with id_token)
+  loginTelegramOIDC: async (
+    idToken: string,
+    campaignSlug?: string | null,
+    referralCode?: string | null,
+  ): Promise<AuthResponse> => {
+    const response = await apiClient.post<AuthResponse>('/cabinet/auth/telegram/oidc', {
+      id_token: idToken,
+      campaign_slug: campaignSlug || undefined,
+      referral_code: referralCode || undefined,
+    });
+    return response.data;
+  },
+
   // Email login
   loginEmail: async (
     email: string,