Add Green Web Foundation badge (#9)

## Summary
- Adds Green Web Foundation badge to README.adoc

## Test plan
- [ ] Verify badge renders correctly on GitHub

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: hyperpolymath

README.adoc

@@ -7,6 +7,7 @@ image:https://img.shields.io/badge/OpenSSF-Best_Practices-green?logo=opensources
 image:https://img.shields.io/badge/License-PMPL--1.0-blue.svg[License: PMPL-1.0,link="https://github.com/hyperpolymath/palimpsest-license"]
 image:https://img.shields.io/badge/Provers-30-green.svg[Provers: 30]
 image:https://img.shields.io/badge/Tests-306%2B-brightgreen.svg[Tests: 306+]
+image:https://api.thegreenwebfoundation.org/greencheckimage/jewell.nexus[Green Hosting,link="https://www.thegreenwebfoundation.org/green-web-check/?url=jewell.nexus"]
 
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