v0.2.0 - Real mixed-SKU optimizer

v0.2.0 - Real mixed-SKU pallet optimizer

First release with a working optimization engine.

• New optimize_pallet() API and palletize-optimize CLI: real shelf-packing
  with rotation, computed volumetric density, density uplift vs a naive baseline,
  and a deterministic stability score (base-support ratio + center-of-mass).
• Dependency-free: pip install palletizer-full-stack.
• 9-test suite; ruff + pytest enforced in CI.

Heuristic v1. An exact solver (OR-Tools CP-SAT) can slot in behind the same API.