* s3api: fail closed when S3 Tables signature verification fails
* s3api: avoid nil Account dereference in S3 Tables auth log
* iceberg: return auth error instead of falling back to DefaultAllow
* lance: return auth error instead of falling back to DefaultAllow
* s3api: stop trusting client-supplied s3-account-id
The header is set by the server after successful authentication; scrub
inbound values alongside the other internal headers, and apply the same
admin guard to the header fallback branch of getAccountID that the
identity branch already has.
* test: cover table-catalog auth wrappers and principal resolution
* test: configure anonymous identity where catalog clients do not sign
* s3api: scrub s3-account-id after signature verification