Fixes#1765Fixes#1771
This PR addresses two issues:
1. CreateBucket was previously allowed when the gateway was running in read-only mode. It is now correctly blocked.
2. Write operations were permitted on public buckets in read-only mode because the public access checks in `auth.VerifyAccess` were evaluated before the read-only check. The read-only check now takes precedence, and all write operations on public buckets are blocked.