Add enterprise cost center chargeback guard

[haocyan0723-code]

/claim #19

This adds a focused cost-center chargeback guard for enterprise tooling.

Scope:

• checks active cost centers
• checks PI approval and grant allowability
• checks allowed expense categories
• checks remaining budget and overage approval
• checks usage evidence and data residency
• returns approve, route for approval, or block decisions
• writes JSON and Markdown review artifacts
• includes MP4 and GIF demo artifacts for review

Validation run locally:

• node enterprise-cost-center-chargeback-guard/test.js
• node enterprise-cost-center-chargeback-guard/demo.js
• node --check enterprise-cost-center-chargeback-guard/index.js

No finance system calls, credentials, real institutional data, payment processing, or external APIs are used.