v3.21.177

Add Playwright visual-regression layer for skins

Parameterised harness (test/visual/harness.html) renders a card or its editor
with a mock hass; skins.spec.mjs screenshots dark/light/HA, a legacy skin, the
inline team names + tracked underline (light + white-gold), and the editor
(swatches desktop/mobile, custom contrast warning, shared inheritance). Baselines
committed (darwin); test:visual script; kept out of npm test (browser-free).
Confirmed light appearance renders correctly (avg brightness 75 vs dark 33).