fix: multi-tariff filter now works server-side + trial-only checkbox

- Send comma-separated tariff_ids to backend (was only single ID)
  — server now filters with IN() operator, pagination correct
- Remove client-side tariff filtering (server handles it)
- Add "Только триал" checkbox filter: amber checkbox, filters users
  with trial subscriptions client-side
- Remove "trial" from status dropdown (was not working via
  subscription_status server filter)
- i18n: trialOnly key (ru + en)

src/locales/ru.json

@@ -3834,6 +3834,7 @@
         "allStatuses": "Все статусы",
         "allTariffs": "Все тарифы",
         "allGroups": "Все группы",
+        "trialOnly": "Только триал",
         "tariffsSelected": "{{count}} тарифов",
         "selectAll": "Выбрать все",
         "deselectAll": "Снять все"