test(glyph): Playwright smoke test for Customize tab on Pie chart

Verifies the GlyphOptionsPanel renderer kicks in end-to-end: creates a
Pie chart via the API, opens its Explore page, switches to the Customize
tab, and asserts a known glyph arg (Show legend) renders. This is the
shortest path to catching a regression in the glyph -> control-panel
hybrid rendering path.

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