chore: RSR compliance — delete AI.djot, rename AI manifest, remove stale files

Automated RSR cleanup:
- Delete AI.djot (superseded by 0-AI-MANIFEST.a2ml)
- Rename AI.a2ml → 0-AI-MANIFEST.a2ml (RSR standard name)
- Delete CONTRIBUTING.adoc (duplicate of CONTRIBUTING.md)
- Delete stale snapshot/status files from root

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

Author: hyperpolymath