Plan step 36. <x-tooltip> renders data-md-tooltip and data-md-side on
the bubble and data-md-tooltip-anchor on a standalone trigger's wrapper;
tooltip.css draws PlainTooltipTokens' inverse-surface bubble, its anchor
placement and flips per side, and the fade on the fast effects spring
with @starting-style.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Qwx5USif3wFFmxtHg5U1g9