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",