integrate: polish from cross-lane audit

Three small adjustments and two new docs.

Adjustments:
  Add *.agdai to .gitignore.

New docs:
  docs/next-questions.adoc unifies open questions across gates
  with stable numbering. Includes gate-1 Q1, gate-2 Q2,
  gate-3 Q3, cross-cutting QC, and EI-1 closed and
  EI-2 initially open, closed in commit 7.

  docs/integration-audit.adoc records the cross-lane audit
  that produced this integration sequence.

Author: hyperpolymath