feat(signal_v2-phase3b): foundation — config + state + requirements

- config.py: CHRONOS_MODEL env (default amazon/chronos-2)
- state.py: PollState extended with daily_ohlcv + chronos_predictions
  + minute_momentum
- requirements.txt: transformers + chronos-forecasting

33 existing tests still pass.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

requirements.txt

@@ -7,3 +7,7 @@ pytest>=8.0
 pytest-asyncio>=0.23
 respx>=0.21
 websockets>=12
+# Phase 3b dependencies (Chronos-2 + ML)
+transformers>=4.40
+chronos-forecasting>=1.4
+# torch: typically already installed via V1 venv; if not, install with CUDA support manually