fix: review findings — polling fallback, sessionStorage cleanup, UX

- Add 5s polling for 90s after opening external browser link (Mini App)
- Show info toast "Continue in browser" when opening external OAuth
- Fix premature sessionStorage cleanup: peek-then-clear pattern
- Use useIsTelegram() hook instead of direct isInTelegramWebApp()
- Add continueInBrowser i18n key (ru, en, zh, fa)

src/locales/en.json

@@ -3618,6 +3618,7 @@
       "linkingTelegram": "Connecting Telegram...",
       "returnToTelegram": "Return to Telegram to continue",
       "openTelegram": "Open Telegram",
+      "continueInBrowser": "Continue authorization in the opened browser",
       "providers": {
         "telegram": "Telegram",
         "email": "Email",

src/locales/fa.json

@@ -3054,6 +3054,7 @@
       "linkingTelegram": "در حال اتصال تلگرام...",
       "returnToTelegram": "برای ادامه به تلگرام بازگردید",
       "openTelegram": "باز کردن تلگرام",
+      "continueInBrowser": "ادامه احراز هویت در مرورگر باز شده",
       "providers": {
         "telegram": "تلگرام",
         "email": "ایمیل",

src/locales/ru.json

@@ -4178,6 +4178,7 @@
       "linkingTelegram": "Привязка Telegram...",
       "returnToTelegram": "Вернитесь в Telegram, чтобы продолжить",
       "openTelegram": "Открыть Telegram",
+      "continueInBrowser": "Продолжите авторизацию в открывшемся браузере",
       "providers": {
         "telegram": "Telegram",
         "email": "Email",

src/locales/zh.json

@@ -3053,6 +3053,7 @@
       "linkingTelegram": "正在关联 Telegram...",
       "returnToTelegram": "返回 Telegram 继续操作",
       "openTelegram": "打开 Telegram",
+      "continueInBrowser": "请在打开的浏览器中继续授权",
       "providers": {
         "telegram": "Telegram",
         "email": "邮箱",