Codex flagged that _buildSkinPicker injected the extension-controlled skin
label/name via btn.innerHTML, so a malicious registerHermesSkin descriptor
(label='<img src=x onerror=...>') could execute when Settings -> Appearance
builds the picker. Rebuild the button with DOM nodes + textContent for the
label and set swatch backgrounds via element.style.background. Adds regression
tests asserting the innerHTML sink is gone.