v0.1.11

• Docs and Playground share one header: same markup (makeHeader() in build/site.mjs), styles (site/shell.css) and theme toggle (site/shell.js). The Playground gains the theme toggle; a test keeps both headers pixel-identical.
• .u-shell-main sets only block padding, so .u-shell-layout keeps its side gutters; .u-shell-header-actions gap is now --u-space-2.
• The Playground preview starts in the page's theme.
• The favicon follows the browser's color scheme (ink U on light, paper U on dark).
• Add uniform-icon-color.svg and its generated uniform-icon-on-dark.svg.
• Tighten the hero spacing; points sit between the lede and the actions.
• Fix the Atmosphere section anchor (#labs-atmosphere), which collided with the background canvas id.
• Playground tests run against the built site.