docs: RFC 0001 - Cross-repo coordination with realms
Add comprehensive design for cross-repo coordination:
- Spike: Initial problem exploration
- Dialogue: 12-expert, 6-round alignment session
- RFC: Full implementation spec
Key design decisions:
- Realm = git repo (auditable, no new infrastructure)
- Index → Realm → Domain → Repo hierarchy
- Export/import contracts with semver
- Pull-based sync with GitHub issue notifications
- Different orgs can coordinate without shared write access
7-week MVP: init, join, export, import, sync, check, status integration
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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