Add revenue tax exemption controls

[zhengjynicolas]

/claim #20

Summary

• Adds a focused institutional tax exemption and grant billing compliance module for Revenue Infrastructure.
• Checks exemption certificate expiry, VAT/reverse-charge evidence, configured tax treatment, grant budget/category controls, settlement reconciliation, billing holds, invoice summaries, and deterministic audit digests.
• Includes sample data, requirement mapping, tests, and a real terminal demo video.

Demo video

• GitHub video: https://github.com/zhengjynicolas/SCIBASE.AI/blob/codex/revenue-tax-exemption-controls-20/revenue-tax-exemption-controls/docs/tax-exemption-demo.mp4
• Raw MP4: https://raw.githubusercontent.com/zhengjynicolas/SCIBASE.AI/codex/revenue-tax-exemption-controls-20/revenue-tax-exemption-controls/docs/tax-exemption-demo.mp4

Verification

• npm run check
• npm test
• npm run demo
• git diff --cached --check
• ffprobe revenue-tax-exemption-controls/docs/tax-exemption-demo.mp4

[zhengjynicolas]

/claim #20