feat: add project structure and basic NNUE model

- Create python directory with data/, model/ subdirectories
- Implement LinearEval(61072->1) model
- Add config, constants, feature_extractor
- Add tests with 4 passing test cases

python/README.md

@@ -0,0 +1,19 @@
+# Chess NNUE Distillation
+
+Train a single linear layer on Stockfish's NNUE features.
+
+## Quick Start
+
+```bash
+cd python
+source .venv/bin/activate
+pip install torch --index-url https://download.pytorch.org/whl/cu121
+pip install numpy python-chess tqdm matplotlib h5py joblib pytest
+python train_full.py
+```
+
+## Architecture
+
+- Input: 61,072 features (352 HalfKAv2_hm + 60,720 FullThreats)
+- Output: 1 scalar (centipawns)
+- Optimizer: Adam (lr=1e-3, wd=1e-4)