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/locales/en.json

@@ -187,7 +187,13 @@
     "forgotPasswordHint": "Enter your email to receive a reset link",
     "loginSuccess": "Login successful",
     "passwordResetSent": "Password reset link sent to your email",
-    "sendResetLink": "Send reset link"
+    "sendResetLink": "Send reset link",
+    "continueWithGoogle": "Continue with Google",
+    "continueWithYandex": "Continue with Yandex",
+    "continueWithDiscord": "Continue with Discord",
+    "continueWithVk": "Continue with VK",
+    "oauthError": "Authorization was denied or failed",
+    "oauthExpired": "OAuth session expired. Please try again."
   },
   "emailVerification": {
     "title": "Email Verification",

src/locales/fa.json

@@ -181,7 +181,13 @@
     "passwordTooShort": "رمز عبور باید حداقل ۸ کاراکتر باشد",
     "sendResetLink": "ارسال لینک بازنشانی",
     "tooManyAttempts": "تلاش‌های زیاد. لطفاً بعداً امتحان کنید",
-    "verificationEmailNotice": "پس از ثبت نام، ایمیل تأیید به آدرس شما ارسال خواهد شد"
+    "verificationEmailNotice": "پس از ثبت نام، ایمیل تأیید به آدرس شما ارسال خواهد شد",
+    "continueWithGoogle": "ادامه با Google",
+    "continueWithYandex": "ادامه با Yandex",
+    "continueWithDiscord": "ادامه با Discord",
+    "continueWithVk": "ادامه با VK",
+    "oauthError": "مجوز رد شد یا ناموفق بود",
+    "oauthExpired": "نشست OAuth منقضی شده است. لطفاً دوباره امتحان کنید."
   },
   "emailVerification": {
     "title": "تایید ایمیل",

src/locales/ru.json

@@ -190,7 +190,13 @@
     "clickLinkToVerify": "Перейдите по ссылке в письме, чтобы подтвердить аккаунт и войти.",
     "backToLogin": "Вернуться ко входу",
     "emailNotVerified": "Сначала подтвердите email",
-    "loginSuccess": "Авторизация успешна"
+    "loginSuccess": "Авторизация успешна",
+    "continueWithGoogle": "Продолжить через Google",
+    "continueWithYandex": "Продолжить через Яндекс",
+    "continueWithDiscord": "Продолжить через Discord",
+    "continueWithVk": "Продолжить через VK",
+    "oauthError": "Авторизация отклонена или не удалась",
+    "oauthExpired": "Сессия OAuth истекла. Попробуйте снова."
   },
   "emailVerification": {
     "title": "Подтверждение email",

src/locales/zh.json

@@ -181,7 +181,13 @@
     "passwordTooShort": "密码至少需要8个字符",
     "sendResetLink": "发送重置链接",
     "tooManyAttempts": "尝试次数过多，请稍后再试",
-    "verificationEmailNotice": "注册后，验证邮件将发送到您的邮箱"
+    "verificationEmailNotice": "注册后，验证邮件将发送到您的邮箱",
+    "continueWithGoogle": "通过 Google 继续",
+    "continueWithYandex": "通过 Yandex 继续",
+    "continueWithDiscord": "通过 Discord 继续",
+    "continueWithVk": "通过 VK 继续",
+    "oauthError": "授权被拒绝或失败",
+    "oauthExpired": "OAuth 会话已过期。请重试。"
   },
   "emailVerification": {
     "title": "邮箱验证",