Design for 3 remaining deferred stubs from 2026-02-24 audit:
- Retrain Model: fine-tune via gRPC with TrainingMode proto field
- Portfolio Positions: PositionProvider trait with broker + DB fallback
- ML Confidence: ensemble RPC with liquidity heuristic fallback
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
