Add AGENTS.md section provenance metadata

[chubes4]

Summary

• Adds owner, freshness, and conditions metadata to the generated Homeboy Codebox AGENTS.md SectionRegistry registration.
• Extends the focused AGENTS.md guidance regression test to assert the new metadata passed to Data Machine.
• Keeps docs/skills unchanged because no old compose --list discovery references were present.

Related: Extra-Chill/data-machine#2486

Verification

• bash tests/agents-md-guidance.sh
• bash -n lib/agents-md-guidance.sh tests/agents-md-guidance.sh
• bash -n **/*.sh
• bash tests/bridge-render.sh
• bash tests/opencode-wrapper-removal.sh
• bash tests/kimaki-agent-fallback.sh

AI assistance

• AI assistance: Yes
• Tool(s): OpenCode (GPT-5.5)
• Used for: Drafted the focused metadata/test changes and ran local verification; Chris remains responsible for review and merge.