Reject informational commands as merge-gate validation evidence

[lamemustafa]

Root cause

A version or help command can satisfy the current syntactic validation-command rule without testing, building, or reproducing behavior.

Rectification

Reject informational invocations and require a test, build, or concrete reproduction target.

Regression check

python3 scripts/merge-gate.test.py

Scope

Deferred from PR #335 under the owner-approved P1-only merge stopping rule.