DOC: Fix mouserotationstyle value for Shoemake's arcball - #32475

PR summary

The "Rotation with mouse" section of doc/api/toolkits/mplot3d/view_angles.rst says Ken Shoemake's arcball is selected with mouserotationstyle: Shoemake. That value is rejected:

>>> mpl.rcParams['axes3d.mouserotationstyle'] = 'Shoemake'
ValueError: Key axes3d.mouserotationstyle: 'Shoemake' is not a valid value
for axes3d.mouserotationstyle; supported values are
['azel', 'trackball', 'sphere', 'arcball']

Shoemake was a valid value while #28841 was in review. Commit 89701eb ("Soften the arcball edge using a 'border' parameter") renamed the styles (arcball → sphere, Shoemake → arcball) and updated the validator, but missed this line. So Shoemake was never valid in a release (3.10.0 already rejects it).

The correct value is arcball. That is what the code runs for this style (axes3d.py, the else: # 'arcball' branch), and the rest of the page agrees: the summary table row, the example comment ('azel', 'trackball', 'sphere', or 'arcball') and the paragraph "Both arcballs (mouserotationstyle: sphere and mouserotationstyle: arcball)". The default matplotlibrc and the 3.10 what's new use arcball too.

This PR corrects it.

AI Disclosure

Claude Code (Claude Sonnet 5.5 (high) ) flagged this issue while reviewing docs.

PR quality check

• Use an expressive title, e.g. "Fix title font property precedence"
• [N/A] New and changed code is tested
• [N/A] Plotting related features are demonstrated in an example
• [N/A] New features and API changes have release notes
• Documentation complies with general and docstring guidelines