fix: select-all subscriptions + per-page selector

- Fix allVisibleSubscriptionIds: include ALL users' filtered subs
  (was only users with >1 subs — single-sub users were excluded)
- Add per-page selector (25/50/100/200) in pagination bar
- Make limit a state variable instead of constant
- perPage i18n keys (ru + en)

src/locales/en.json

@@ -2031,6 +2031,7 @@
       "selectUser": "Select user {{name}}",
       "deselectUser": "Deselect user {{name}}",
       "noResults": "No users found",
+      "perPage": "Per page",
       "actions": {
         "extend": "Extend subscription",
         "cancel": "Deactivate subscriptions",