Regenerate baseline images via test framework

Baseline images must be generated through PlotTester.compare() which
applies set_size_inches, bbox_inches='tight', and _resize_and_pad_image
to produce exactly (400, 300) px outputs. Previous baselines were saved
manually with fig.savefig(dpi=80) yielding (512, 384) px.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: timtreis