[sciabarracom]

Follow-up to #109, which validated spec.namespace but left two other tenant controlled WhiskUser fields flowing unsanitized into shell commands executed inside the data pods via kubectl exec.

• spec.postgres.database reached bash -c "... psql --dbname {db_name}" in exec_psql_command_in_db. Unlike the namespace field it never becomes a filename, so it was not even constrained to path safe characters.
• spec.object-storage.{data,route}.bucket reached sh -c "echo '{command}' | weed shell" in the seaweedfs client, where a quote breaks out of the single quoted string.

Adds util.validate_database_name and util.validate_bucket_name next to the existing validate_namespace and applies them at the call sites and at the shell sinks, plus matching CEL rules on the CRD so the API server rejects the payload before the operator sees it. The regexes and the CEL rules were cross checked to accept exactly the same inputs.

Also:

• guards the latent render_kvrocks_script / exec_kvrocks_command pair, which repeats the same pattern but is not currently wired into the user path
• makes validate_namespace return False for non string input instead of raising TypeError
• corrects a copy pasted error message referring to exec_mongosh_command inside exec_psql_command

[sciabarracom]

built and tested