fix(steps): anchor the empty-step-content :has to the step item

[lucaspunz]

Summary

Removes both sources of universal-subject :has() selectors, which force whole-document style recalc on every DOM mutation in consumers:

• Steps: group-has-[...]/step:hidden re-anchored to the step item: [[role=listitem]:has(…)_&]:hidden.
• code.css: the two bare :has(…) > [data-component-part=code-block-root] padding rules could only ever match the CodeBlock root div, which already knows at render time whether it has a header or floating buttons — the root now stamps data-has-header / data-has-floating-buttons and the rules anchor to those. CodeGroup never matched either rule.

Biome GritQL plugins ban both shapes from returning: group-has- in JS/TSX strings, bare :has( selectors in css (anchored :has stays allowed).

Consumer impact: perf-only; the DOM gains one inert data-has-* attribute on the CodeBlock root (snapshot-test churn at bump time).

Test Plan

• pnpm build: no group-has or universal-subject :has( anywhere in dist
• pnpm lint:check green; both plugins fire on synthetic violations, silent on anchored :has
• rendered behavior unchanged: connector hidden on empty step content; code padding identical across header/floating-button/group variants

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Note

Low Risk
Performance-oriented selector and attribute changes with no intended behavior change; only an extra inert data-has-* on CodeBlock roots for consumers.

Overview
Eliminates universal-subject :has() patterns that trigger expensive whole-document style recalc on DOM mutations in consuming apps.

Steps: The last-step connector hide rule drops group-has-…/step in favor of an ancestor-anchored variant: [[data-component-part=step-item]:has([data-component-part=step-content]:empty)_&]:hidden (same UX: line hidden when step content is empty).

Code blocks: code.css no longer uses bare :has(…) for padding; the CodeBlock root now sets data-has-header or data-has-floating-buttons at render time, and CSS targets those attributes instead.

Lint: Two Biome Grit plugins block regressions—group-has- in class strings and universal-subject :has( in CSS (anchored :has remains allowed).

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