* iceberg: return 400 for invalid namespace/table names
The S3 Tables name charset (a-z, 0-9, _) is stricter than the Iceberg
REST spec, so clients sending hyphens or uppercase hit a validation
error. That error fell through to 500; it's client input, so map it to
400 BadRequestException across the namespace and table handlers.
* iceberg: tighten name-validation error matching
Match the validator's own phrasings (invalid/must/cannot) instead of a
bare "namespace name"/"table name" substring, so an unrelated fault that
happens to mention a name isn't misreported as a 400. Lowercase first to
stay robust to message capitalization.
Chris LuandGitHub
6de283ccaa