fix(cabinet): recover "Сервис недоступен" false-positive + top-up fixes

- health probe: tolerant timeout (12s) + retry before flagging the backend down. A
  hardcoded 5s probe racing auth bootstrap falsely showed ServiceUnavailableScreen on
  slow devices / cold mobile connections while the 30s API requests would have
  succeeded ("works on one device, not another on the same Wi-Fi"). The recovery poll
  self-reschedules with the tolerant timeout so slow devices auto-recover.
- TopUpAmount: fetch payment methods with a real query (fixes the infinite spinner on a
  cold cache / browser-back) and use canonical RUB for quick-amount chips so FX rounding
  can't reject a min-amount selection in non-RUB locales.
- settings UI: render secret values as a masked password input (pairs with the backend
  secret masking); leaving the field empty keeps the stored secret.
- deps: npm audit fix (18 -> 5 advisories).

Also bundles in-progress settings env-lock UI work.

src/locales/ru.json

@@ -2027,6 +2027,8 @@
       "quickToggles": "Быстрые переключатели",
       "modified": "Изменено",
       "readOnly": "Только чтение",
+      "envLocked": "Задано в .env",
+      "envLockedHint": "Значение задано в файле .env и перекрывает базу данных — здесь его изменить нельзя. Чтобы управлять настройкой из кабинета, удалите ключ из .env и перезапустите бота.",
       "badgeDb": "БД",
       "badgeEnv": "ENV",
       "reset": "Сбросить",