Adds external comparison table (WAI-ARIA / React Aria / Ark UI / Base UI / Bits) with sources and a Gaps table with disposition markers, bringing the css-field audit scorecard to parity with number-field (only the systemic E-2.2 css-import rule + R-1.3 readonly warning remain, both shared with the reference component). Smoke PASS for /uix/components/css-field.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
