feat: add rig management package
Types:
- Rig: managed repository with polecats, witness, refinery, mayor
- RigSummary: concise rig overview
- Manager: rig discovery, loading, creation
Manager operations:
- DiscoverRigs: load all registered rigs
- GetRig: get specific rig by name
- RigExists, ListRigNames: query helpers
- AddRig: clone and register new rig
- RemoveRig: unregister rig (keeps files)
Rig structure follows docs/architecture.md:
- polecats/, refinery/rig/, witness/rig/, mayor/rig/
Closes gt-u1j.5
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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