fix(desktop): pre-check backend updates in poller; client button first

Two follow-ups from testing the two-button bar:

- The background poller and focus handler only checked the client, so the
  backend behind-count and changelog stayed empty until the user opened the
  overlay — and the overlay's first render then hit the empty-commits fallback
  ('Improvements and fixes') instead of the real changelog. Check the backend
  alongside the client on poller start, interval, and focus so its state is
  ready before the button is clicked.
- Order the status bar client-first, backend-second.

apps/desktop/src/app/shell/hooks/use-statusbar-items.tsx

@@ -442,8 +442,8 @@ export function useStatusbarItems({
               variant: 'action' as const
             })
       },
-      ...(backendVersionItem ? [backendVersionItem] : []),
-      clientVersionItem
+      clientVersionItem,
+      ...(backendVersionItem ? [backendVersionItem] : [])
     ],
     [
       busy,