[AIAA] Build step 10: participant guide

Build step 10 (spec section 16, PR #363): `docs/assessment-guide.md`,
the lifecycle from the outside, one page for the three audiences the
system asks something of (section 13). Late in the order on purpose: it
documents the system that then exists.

Done when:

- [ ] Review confirms every ask the lifecycle makes of a requester,
stakeholder, or operator appears with the section 12 behavior it
triggers, including the by-hand procedure a failed workflow
falls back to (HC-4).
- [ ] It references the methodology rather than restating it (P-2).

The pilot is its live test: a participant who needs an ad hoc
explanation has found a guide defect; recorded here.