feat(admin): Add group filtering for account listings

- Add groupID parameter to ListAccounts and ListWithFilters methods
- Implement account filtering by group ID in repository query
- Add group query parameter parsing in account handler
- Update all ListAccounts/ListWithFilters call sites with groupID parameter
- Add group filter UI component to AccountTableFilters
- Add i18n translations for group filter label in English and Chinese
- Update API contract and test stubs to reflect new signature
- Enable filtering accounts by their assigned groups in admin panel

frontend/src/views/admin/AccountsView.vue

@@ -6,6 +6,7 @@
           <AccountTableFilters
             v-model:searchQuery="params.search"
             :filters="params"
+            :groups="groups"
             @update:filters="(newFilters) => Object.assign(params, newFilters)"
             @change="debouncedReload"
             @update:searchQuery="debouncedReload"
@@ -439,7 +440,7 @@ const isColumnVisible = (key: string) => !hiddenColumns.has(key)
 
 const { items: accounts, loading, params, pagination, load, reload, debouncedReload, handlePageChange, handlePageSizeChange } = useTableLoader<Account, any>({
   fetchFn: adminAPI.accounts.list,
-  initialParams: { platform: '', type: '', status: '', search: '' }
+  initialParams: { platform: '', type: '', status: '', group: '', search: '' }
 })
 
 const isAnyModalOpen = computed(() => {