fix(clients): persist sort selection across navigation

The clients page saved searchKey and filters to localStorage but not
the sort selection, so leaving the page and returning reset sort to the
default (Oldest). Persist the chosen sort alongside the existing filter
state and restore it on mount, matching the filter-persistence pattern.

frontend/.gitignore

@@ -1,3 +1,4 @@
 node_modules/
 .vite/
 *.log
+*.tsbuildinfo

frontend/src/pages/clients/ClientsPage.tsx

@@ -115,6 +115,7 @@ type Bucket = 'active' | 'deactive' | 'depleted' | 'expiring';
 interface PersistedFilterState {
   searchKey: string;
   filters: ClientFilters;
+  sort: string;
 }
 
 const INBOUND_PROTOCOL_COLORS: Record<string, string> = {
@@ -145,9 +146,10 @@ function readFilterState(): PersistedFilterState {
         inboundIds: Array.isArray(fromRaw.inboundIds) ? fromRaw.inboundIds : [],
         groups: Array.isArray(fromRaw.groups) ? fromRaw.groups : [],
       },
+      sort: typeof raw.sort === 'string' ? raw.sort : '',
     };
   } catch {
-    return { searchKey: '', filters: emptyFilters() };
+    return { searchKey: '', filters: emptyFilters(), sort: '' };
   }
 }
 
@@ -224,8 +226,9 @@ export default function ClientsPage() {
   const [filters, setFilters] = useState<ClientFilters>(initial.filters);
   const [filterDrawerOpen, setFilterDrawerOpen] = useState(false);
 
-  const [sortColumn, setSortColumn] = useState<string | null>(DEFAULT_SORT.column);
-  const [sortOrder, setSortOrder] = useState<'ascend' | 'descend' | null>(DEFAULT_SORT.order);
+  const initialSort = SORT_OPTIONS.find((o) => o.value === initial.sort) ?? DEFAULT_SORT;
+  const [sortColumn, setSortColumn] = useState<string | null>(initialSort.column);
+  const [sortOrder, setSortOrder] = useState<'ascend' | 'descend' | null>(initialSort.order);
   const [currentPage, setCurrentPage] = useState(1);
   const [tablePageSize, setTablePageSize] = useState(25);
   // debouncedSearch lags behind the input so we don't spam the server on every
@@ -233,8 +236,8 @@ export default function ClientsPage() {
   const [debouncedSearch, setDebouncedSearch] = useState(searchKey);
 
   useEffect(() => {
-    localStorage.setItem(FILTER_STATE_KEY, JSON.stringify({ searchKey, filters }));
-  }, [searchKey, filters]);
+    localStorage.setItem(FILTER_STATE_KEY, JSON.stringify({ searchKey, filters, sort: sortValueFor(sortColumn, sortOrder) }));
+  }, [searchKey, filters, sortColumn, sortOrder]);
 
   useEffect(() => {
     const handle = window.setTimeout(() => setDebouncedSearch(searchKey), 300);