feat: multi-tariff bulk actions UI — subscription-level selection

- Detect multi-tariff mode when users have multiple subscriptions
- Expandable user rows with chevron: click to show subscription sub-rows
- Each subscription sub-row shows: tariff name, status badge, days
  remaining (color-coded green/amber/red), traffic progress bar
- Independent subscription checkboxes for subscription-level actions
- FloatingActionBar shows dual counters: users (accent) + subscriptions
  (green), actions grouped by target type with disabled state
- Subscription-level actions send subscription_ids, user-level send
  user_ids to the backend
- Backward compatible: single-tariff mode unchanged (no chevrons,
  no sub-rows, user-only selection)
- i18n: subscriptionsSelected, usersSelected, expand/collapse,
  daysUnit, trafficOf, trafficGbUnit (ru + en)

src/api/adminUsers.ts

@@ -33,6 +33,17 @@ export interface UserPromoGroupInfo {
   is_default: boolean;
 }
 
+export interface UserListItemSubscription {
+  id: number;
+  tariff_id: number | null;
+  tariff_name: string | null;
+  status: string;
+  end_date: string | null;
+  days_remaining: number;
+  traffic_used_gb: number;
+  traffic_limit_gb: number;
+}
+
 export interface UserListItem {
   id: number;
   telegram_id: number;
@@ -62,6 +73,7 @@ export interface UserListItem {
   has_restrictions: boolean;
   restriction_topup: boolean;
   restriction_subscription: boolean;
+  subscriptions?: UserListItemSubscription[];
 }
 
 export interface UsersListResponse {