Phase 1b: React Query + Vitest on client

- @tanstack/react-query v5 with QueryClientProvider at app root
- client/src/api/queries.ts: query-key factory, hooks for tickets, ticket, audit,
  comments, users, CTI tree + cascade, plus full mutation set
  (create/update/delete ticket, add/delete comment, CTI CRUD, user CRUD)
- All page-level useEffect + useState fetching replaced:
  Dashboard, MyTickets, TicketDetail, NewTicket, admin/CTI, admin/Users
- Dashboard preserves 300ms debounced search via separate debouncedSearch state
- CTISelect cascades via useCategories / useTypes(categoryId) / useItems(typeId);
  dependent hooks disabled until parent selected
- vitest + @testing-library/react + jsdom; 6 client tests cover SeverityBadge + StatusBadge

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

client/src/api/queryClient.ts

@@ -0,0 +1,11 @@
+import { QueryClient } from '@tanstack/react-query';
+
+export const queryClient = new QueryClient({
+  defaultOptions: {
+    queries: {
+      retry: 1,
+      staleTime: 30 * 1000,
+      refetchOnWindowFocus: false,
+    },
+  },
+});