Release v0.2.0: aligned_lambdas (#94) + version bump (#161)

Adds proxy-eigenvalue correspondence for Procrustes-aligned gradients,
the last unaddressed item from #94:

- procrustes() gains return_transform=True
- procrustes_alignment() gains return_transforms=True
- ProcrustesAlignment now exposes transforms_
- New helper aligned_lambdas(lambdas, transform) using the largest
  |transform[i,j]| heuristic suggested by @OualidBenkarim
- GradientMaps.aligned_lambdas_ exposes the per-dataset proxy lambdas

Bumps version to 0.2.0 and writes a detailed CHANGELOG entry covering
every change since 0.1.22 (issues, packaging, CI, docs, tests, MATLAB
fix). 165 tests passing, 76% line coverage.