fix: keep ghost payment identifiers collision-free

[rogerchappel]

Summary

• add regression coverage for collisions with PAY-GHOST-9001, INV-NOT-FOUND, and VEN-404
• allocate unique payment and deliberately missing relationship identifiers
• keep expected finding evidence synchronized with generated identifiers
• document the scenario behavior change

Commits

• cf70b27 test: cover ghost payment identifier collisions
• e408190 fix: allocate ghost payment identifiers safely
• 9868459 docs: note collision-safe ghost payments

Verification

• node --test tests/scenarios.test.js
• npm run release:check
• git diff --check

All 48 tests pass; syntax, CLI smoke, documentation install smoke, and package dry run pass.

[rogerchappel]

Automated merge note

Triage class: auto-merge

Summary: Makes the ghost-payment scenario allocate collision-free payment and missing-reference identifiers, with regression coverage and a changelog note (3 files, +59/-2).

Checks run: CI / Repository hygiene — SUCCESS; contributor verification: node --test tests/scenarios.test.js (9/9), npm run release:check (48/48 tests, CLI/docs/package smoke), and git diff --check; final diff, mergeability, branch protection, and all Roger Chappel author/committer identities re-verified.

Rebased/CI-repaired: no.

Verified head SHA: 9868459.