holbuild v0.8.1

co-authored by gpt 5.5

What's Changed

• Work on checkpoint budget issues by @xrchz in #82
• Add hbx cache archive helpers by @charles-cooper in #65
• Add hbx export/import commands by @charles-cooper in #66
• Enrich hbx archive manifests by @charles-cooper in #84
• Emit hbx registry metadata sidecars by @charles-cooper in #85
• Document hbx release registry workflow by @charles-cooper in #86

Full Changelog: v0.8.0...v0.8.1