feat: multi-select tariff filter, select-all subscriptions, auto-expand

1. Tariff filter: replace single-select dropdown with MultiSelectDropdown
   component — checkboxes for each tariff, "Select all" / "Deselect all"
   controls, shows selected names or count in button label
2. Client-side subscription filtering: when tariffs selected in filter,
   only show matching subscriptions in expanded sub-rows
3. "Select all subscriptions" button in FloatingActionBar — toggles all
   visible subscription checkboxes and auto-expands relevant rows
4. Auto-expand: all user rows with multiple subscriptions are expanded
   by default when data loads (no need to click chevron)
5. i18n: new keys for tariff multi-select and subscription select-all

src/locales/en.json

@@ -2078,7 +2078,10 @@
         "promoGroup": "Promo group",
         "allStatuses": "All statuses",
         "allTariffs": "All tariffs",
-        "allGroups": "All groups"
+        "allGroups": "All groups",
+        "tariffsSelected": "{{count}} tariffs",
+        "selectAll": "Select all",
+        "deselectAll": "Deselect all"
       },
       "statuses": {
         "active": "Active",
@@ -2105,7 +2108,9 @@
       "userTarget": "Target: users",
       "daysUnit": "d",
       "trafficOf": "of",
-      "trafficGbUnit": "GB"
+      "trafficGbUnit": "GB",
+      "selectAllSubs": "Select all subscriptions",
+      "deselectAllSubs": "Deselect all subscriptions"
     },
     "theme": {
       "accentColor": "Accent color",