feat: Concept hierarchy (Phase 5D) - ConceptPath, source schemes, AliasStore
Implements hierarchical subject identifiers with scheme-based source tier inference:
- ConceptPath type with parse/wire_format, leaf/parent, prefix matching
- SourceScheme registry mapping schemes to default SourceClass tiers:
- rfc://, fda://, ietf:// → Regulatory (Tier 0)
- peer://, pubmed:// → PeerReviewed (Tier 1)
- code://, wiki:// → Expert (Tier 3)
- blog://, anon:// → Anecdotal (Tier 5)
- AliasStore for cross-scheme entity resolution (bidirectional indexing)
- API endpoints for concept operations
- Battery tests 8, 9 & 10 for concepts, aliases, and advanced signatures
- Go SDK updates for concept types and signing
Completes Phase 5, advancing to Phase 6 (Distributed Writes).
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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