feat: add Telegram account linking UI with CSRF protection

- TelegramLinkWidget component with Login Widget for browser users
- One-click initData linking for Mini App users
- LinkTelegramCallback page with CSRF state validation
- URL credential clearing via history.replaceState
- Merge flow support with replace navigation
- i18n keys for all 4 locales (ru, en, zh, fa)

src/locales/en.json

@@ -3615,6 +3615,8 @@
       "unlinkError": "Failed to disconnect account",
       "goToAccounts": "Connected Accounts",
       "linking": "Linking account...",
+      "linkTelegramWidget": "Sign in with Telegram to connect",
+      "linkingTelegram": "Connecting Telegram...",
       "providers": {
         "telegram": "Telegram",
         "email": "Email",