Add cancellation effective-date guard

[Entr0zy]

Summary

• Adds a focused subscription cancellation effective-date guard for issue Revenue Infrastructure #20 Revenue Infrastructure.
• Detects late cancellation notice, unapproved effective-date changes, scheduled renewal invoices after cancellation, refund review gaps, compute-credit overhang, analytics export overhang, and missing institutional PO closeout evidence.
• Includes deterministic synthetic sample data plus JSON, Markdown, and SVG reviewer artifacts.

/claim #20

Validation

• node subscription-cancellation-effective-date-guard/test.js
• node subscription-cancellation-effective-date-guard/demo.js
• git diff --check

Demo artifacts

• subscription-cancellation-effective-date-guard/reports/cancellation-packet.json
• subscription-cancellation-effective-date-guard/reports/cancellation-report.md
• subscription-cancellation-effective-date-guard/reports/summary.svg

Deconfliction

This is scoped to post-cancellation effective-date and entitlement wind-down controls. It is separate from renewal notice, trial/promotion, dunning entitlement hold, plan downgrade, payment authorization, account transfer, collections, receipt privacy, sanctions/export, quote approval, and analytics seat roster slices.

Demo artifacts

• subscription-cancellation-effective-date-guard/reports/demo.webm