Add invoice three-way match skill

[zdfgu113]

Adds a public runx skill package for invoice intake and three-way matching.

Final verification:

• Registry package: zdfgu113/invoice-three-way-match@sha-1ec6eb042dde
• Public URL: https://runx.ai/x/zdfgu113/invoice-three-way-match@sha-1ec6eb042dde
• Source commit: 03affb3b0922c40d2c55a00df3e22ecfa0b47a02
• Local harness: 2/2 passed
• Hosted/installed harness: 2/2 passed
• Exact runx --version output captured in evidence: runx-cli 0.6.13
• Dogfood block is compact and includes package, input, command, receipt_ref, verify_verdict, and harness_cases
• Post-publish dogfood receipt: sha256:26e87ba07f05ae0f02e9b3a8e068417e0a473bb6be888eb29b16d134a0062e6b
• Receipt verification: valid, no findings

Artifact refs:

• x_yaml: https://raw.githubusercontent.com/zdfgu113/runx/03affb3b0922c40d2c55a00df3e22ecfa0b47a02/skills/invoice-three-way-match/X.yaml
• skill_md: https://raw.githubusercontent.com/zdfgu113/runx/03affb3b0922c40d2c55a00df3e22ecfa0b47a02/skills/invoice-three-way-match/SKILL.md
• evidence_json: https://raw.githubusercontent.com/zdfgu113/runx/03affb3b0922c40d2c55a00df3e22ecfa0b47a02/skills/invoice-three-way-match/references/evidence.json
• verification_json: https://raw.githubusercontent.com/zdfgu113/runx/03affb3b0922c40d2c55a00df3e22ecfa0b47a02/skills/invoice-three-way-match/references/published-verification.json
• report: https://raw.githubusercontent.com/zdfgu113/runx/03affb3b0922c40d2c55a00df3e22ecfa0b47a02/skills/invoice-three-way-match/references/report.md

Safety boundary: the skill emits a gated payment approval proposal for settle-invoice; it does not move money or call any payment rail.