The convergence loop now ensures the pair starts with its short side
parallel to the primary axis, maximizing the number of pairs that fit.
Also adds ConvergeStripeAngleShrink to try N+1 narrower pairs, and
evaluates both expand and shrink results to pick the better grid.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
