Replace baseline images with Linux/CI-generated versions

Initial baselines were generated on macOS/arm64. Matplotlib anti-aliasing
produces subtly different output on Linux, causing CI failures with RMS
values 27-37 (tolerance 15). CI-generated images are byte-identical across
Python 3.11, 3.14-stable, and 3.14-pre.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: timtreis