Expand smoke test assertions with full STS specs and ConfigMap snapshots

  30-assert now includes args, imagePullPolicy, defaultMode, and all
  container specs for the three HDFS StatefulSets. 31-assert is refactored
  to diff ConfigMap data against external snapshot files using envsubst and
  yq normalisation, replacing the previous inline envOverrides checks.

  Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: adwk67