fix: preserve generated scenario fixture invariants

[rogerchappel]

Summary

• allocate deterministic collision-free invoice and payment identifiers for generated scenarios
• keep weekend-rush invoice/payment vendor relationships consistent when reserved IDs already exist
• create valid VEN-ORBIT support data for round-dollar-split on empty fixtures
• document deterministic identifier suffixing for custom fixtures

Commits

• bdcd4bf test: cover scenario identifier collisions
• 2fb4e3f fix: preserve generated fixture invariants
• 576c779 docs: define scenario identifier allocation

Verification

• npm ci --ignore-scripts --no-audit --no-fund
• npm run release:check (42/42 tests, syntax, CLI smoke, docs install smoke, package dry-run)
• git diff --check

All commit authors and committers were verified as Roger Chappel miscanalysis@gmail.com.

[rogerchappel]

Automated merge note

Triage class: auto-merge

Summary: Preserves custom-fixture scenario invariants with collision-safe identifiers, valid supporting rows, regression coverage, and documentation (3 files, +62/-12).

Checks run: GitHub CI Repository hygiene SUCCESS; isolated npm run release:check passed (12 tests, syntax, smoke, package dry-run); git diff --check passed; final diff, mergeability, branch protection, commit identities, and head SHA reverified.

Rebased/CI-repaired: No.

Verified head SHA: 576c7798ae21d3328d50b3a7ac7b56578398c707.