fix: drawer open/close updates UI immediately without refresh

- Return null instead of throwing on 404 for drawer current query
- Sync drawer session ID to null when drawer closes
- Await query invalidation before closing dialog
- Fix unused approvedBy lint error

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/admin/src/components/pos/pos-register.tsx

@@ -44,6 +44,8 @@ export function POSRegister() {
   useEffect(() => {
     if (drawer?.id && drawer.status === 'open') {
       setDrawerSession(drawer.id)
+    } else {
+      setDrawerSession(null)
     }
   }, [drawer, setDrawerSession])