fix(frontend): comprehensive i18n cleanup and Select component hardening

frontend/src/components/common/GroupSelector.vue

@@ -1,8 +1,8 @@
 <template>
   <div>
     <label class="input-label">
-      Groups
-      <span class="font-normal text-gray-400">({{ modelValue.length }} selected)</span>
+      {{ t('admin.users.groups') }}
+      <span class="font-normal text-gray-400">{{ t('common.selectedCount', { count: modelValue.length }) }}</span>
     </label>
     <div
       class="grid max-h-32 grid-cols-2 gap-1 overflow-y-auto rounded-lg border border-gray-200 bg-gray-50 p-2 dark:border-dark-600 dark:bg-dark-800"
@@ -32,7 +32,7 @@
         v-if="filteredGroups.length === 0"
         class="col-span-2 py-2 text-center text-sm text-gray-500 dark:text-gray-400"
       >
-        No groups available
+        {{ t('common.noGroupsAvailable') }}
       </div>
     </div>
   </div>