feat: add channel edit in admin, hide subscribed channels in blocking screen

- Admin panel: added Edit button on channel cards with inline edit form
  (title, link, sort order) using existing PATCH API
- Subscription screen: filter out already-subscribed channels so users
  only see what they still need to subscribe to
- Updated channelIdHint to remove @username reference (numeric only)
- Added i18n keys: edit, editing, form.save (en/ru/fa/zh)

src/locales/ru.json

@@ -1334,16 +1334,19 @@
       "disabled": "Отключён",
       "enable": "Включить",
       "disable": "Отключить",
+      "edit": "Изменить",
+      "editing": "Редактирование",
       "delete": "Удалить",
       "deleteConfirm": "Удалить этот канал?",
       "sortOrder": "Порядок",
       "form": {
         "title": "Название",
         "channelId": "ID канала",
-        "channelIdHint": "@username или -100XXXXXXXXXX",
+        "channelIdHint": "-100XXXXXXXXXX",
         "channelLink": "Ссылка на канал",
         "channelLinkHint": "https://t.me/channel",
         "submit": "Добавить",
+        "save": "Сохранить",
         "cancel": "Отмена"
       }
     },