MPSBoost 0.1.0a0 Release Audit

0.1.0a0 reserved the mpsboost package namespace and published the planned public API surface. It was an alpha placeholder release for project discovery and dependency metadata, not a functional training release.

Included:

• package namespace reservation;
• initial sklearn/XGBoost-style API direction;
• backend diagnostics and cache-path planning;
• explicit failure for training operations outside the alpha scope.

Not included:

• real training;
• real MPS kernels;
• model persistence;
• performance claims.