feat: Complete Phase 2 (The Cortex) - query, lens, and API layers
This commit adds the read path (Cortex) to complement the write path (Spine):
## Crates
- stemedb-api: HTTP API with axum + utoipa OpenAPI
- /v1/assert, /v1/query, /v1/epoch, /v1/skeptic, /v1/trace, /v1/audit
- Metered endpoints with quota enforcement
- Ed25519 signature verification
- stemedb-lens: Truth resolution lenses
- RecencyLens, ConsensusLens, ConfidenceLens
- VoteAwareConsensusLens (Ballot Box pattern)
- TrustAwareAuthorityLens (The Hive pattern)
- SkepticLens (conflict analysis)
- EpochAwareLens (paradigm-safe queries)
- stemedb-query: Query engine with materialized views
## Storage Extensions
- VoteStore: Vote aggregation with cached counts
- TrustRankStore: Agent reputation with decay
- AuditStore: Query audit trail
- IndexStore: SP/P/S index structures
- SupersessionStore: Epoch supersession chains
## SDKs
- sdk/go/steme: Go HTTP client with Ed25519 signing
- sdk/go/adk: ADK-Go tools for AI agents
## Documentation
- Updated CLAUDE.md, architecture.md, roadmap.md
- New ai-lookup entries for all services
- Use case docs for consumer health intelligence
- Arena roadmap for simulation advancement
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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