docs: add RFC-0140 Libertaria SSI Stack specification
Complete Self-Sovereign Identity stack specification:
- Four Pillars: Communication, Contracts/Law, Economy, Decentralized Production
- L0-L4 Architecture: SoulKey + QVL / VC Layer / State Channels / Chapter Federation
- did:libertaria method spec with versioning (?versionId= fallback)
- Comparison table: Libertaria vs blockchain SSI systems
- Security & Privacy considerations
- Implementation status and roadmap
Key differentiators documented:
- No blockchain required
- Offline-first operation
- Exit as architectural primitive
- Kenya Rule compliant
Refs: IOP Morpheus lineage, W3C DID/VC compatibility
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