feat: add OAuth 2.0 login UI (Google, Yandex, Discord, VK)

- Add OAuthProvider type and extend User.auth_type union
- Add OAuth API methods (providers, authorize, callback)
- Add loginWithOAuth to auth store
- Create OAuthCallback page with state validation
- Create OAuthProviderIcon component with brand SVGs
- Add OAuth buttons to Login page between Telegram and Email
- Add OAuth callback route to App.tsx
- Add translations for ru, en, zh, fa

src/api/client.ts

@@ -74,6 +74,7 @@ const AUTH_ENDPOINTS = [
   '/cabinet/auth/refresh',
   '/cabinet/auth/password/forgot',
   '/cabinet/auth/password/reset',
+  '/cabinet/auth/oauth/',
 ];
 
 function isAuthEndpoint(url: string | undefined): boolean {