feat(clients): show filtered count in clients list

Surface a "Showing X of Y" counter in the clients filter bar that appears whenever a search term or any filter is active, using the server-provided filtered and total counts. Added the showingCount string across all 13 locales.

Closes #4808

frontend/src/pages/clients/ClientsPage.css

@@ -33,6 +33,13 @@
   flex: 0 0 auto;
 }
 
+.filter-count {
+  margin-inline-start: auto;
+  color: var(--ant-color-text-secondary);
+  font-size: 13px;
+  white-space: nowrap;
+}
+
 .filter-chips {
   display: flex;
   flex-wrap: wrap;

frontend/src/pages/clients/ClientsPage.tsx

@@ -188,7 +188,7 @@ export default function ClientsPage() {
   useEffect(() => { setMessageInstance(messageApi); }, [messageApi]);
 
   const {
-    clients, filtered,
+    clients, total, filtered,
     summary: serverSummary,
     allGroups,
     setQuery,
@@ -993,6 +993,11 @@ export default function ClientsPage() {
                             {t('pages.clients.clearAllFilters')}
                           </Button>
                         )}
+                        {(activeCount > 0 || debouncedSearch.trim().length > 0) && (
+                          <span className="filter-count">
+                            {t('pages.clients.showingCount', { shown: filtered, total })}
+                          </span>
+                        )}
                       </div>
 
                       {activeCount > 0 && (