[AIAA] Build step 11: approver-independence check (advisory)

[nate-double-u]

Build step 11 (spec section 16, PR #363), advisory: a check that
comments when a phase's approver also drafted or reviewed that phase
(sections 4, 10, 12). It never blocks.

Done when one of:

• It flags a staged violation.
• It is explicitly deferred, with the decision recorded here.