feat(web): add React Query, dark mode toggle, and error retry UX

- Install @tanstack/react-query with exponential backoff retry config
- Create QueryClientProvider and custom hooks for listings, analytics,
  payments, and subscription API calls
- Migrate 5 dashboard pages from useState/useEffect to React Query hooks
- Add dark mode CSS variables and ThemeProvider with localStorage persistence
- Add theme toggle button in dashboard header (sun/moon icon)
- Enhance error boundaries with auto-retry, retry count, and loading state

Co-Authored-By: Paperclip <noreply@paperclip.ing>

apps/web/lib/hooks/use-listings.ts

@@ -0,0 +1,23 @@
+import { useQuery } from '@tanstack/react-query';
+import { listingsApi, type SearchListingsParams } from '@/lib/listings-api';
+
+export const listingsKeys = {
+  all: ['listings'] as const,
+  search: (params: SearchListingsParams) => ['listings', 'search', params] as const,
+  detail: (id: string) => ['listings', 'detail', id] as const,
+};
+
+export function useListingsSearch(params: SearchListingsParams = {}) {
+  return useQuery({
+    queryKey: listingsKeys.search(params),
+    queryFn: () => listingsApi.search(params),
+  });
+}
+
+export function useListingDetail(id: string) {
+  return useQuery({
+    queryKey: listingsKeys.detail(id),
+    queryFn: () => listingsApi.getById(id),
+    enabled: !!id,
+  });
+}