* admin: offer copyable S3 object URLs in the bucket file browser
* admin: hide object urls when the bucket type lookup fails
* admin: ignore an s3.public_endpoint that is not an absolute http url
* mini: build the seeded s3 endpoint with JoinHostPort for ipv6
* admin: reject a query or fragment in s3.public_endpoint
* mini: drop the seeded s3 endpoint when a later run disables s3
* admin: reject userinfo and bare delimiters in s3.public_endpoint, redact the warning
* mini: pass its s3 endpoint as an admin option instead of mutating viper
* admin: keep the rejected s3.public_endpoint value out of the log