refactor(theme): move CSS custom property defaults to :root

[ankit-thesys]

Summary

• Move all --openui-* CSS custom property defaults from inline var() fallbacks to a single :root block in a new auto-generated openui-defaults.scss
• Simplify cssUtils.scss variables to bare var(--openui-*) without fallbacks
• Include :root defaults in the bundled components.css via @use in index.scss
• Export ./defaults.css for consumers using individual component CSS imports

Motivation

Previously every var() call in compiled CSS carried an inline fallback value, duplicated across all 50+ component stylesheets. This change:

• Produces cleaner, smaller compiled CSS
• Establishes a single source of truth for default token values
• Follows the standard CSS custom property pattern (:root defaults, scoped overrides)
• ThemeProvider continues to override at body/scoped selectors which naturally cascade over :root

Files changed

File	Change
src/scripts/generate-css-utils.ts	Generates both cssUtils.scss (no fallbacks) and openui-defaults.scss (:root block)
src/cssUtils.scss	(auto-generated) Simplified var() calls
src/openui-defaults.scss	NEW (auto-generated) :root { --openui-*: defaults }
src/components/index.scss	@use "../openui-defaults.scss" at top
src/scripts/scss-import.js	Prepends defaults @use when regenerating
cp-css.js	Copies openui-defaults.css to dist/styles/
package.json	Added ./defaults.css export

Test plan

• pnpm --filter @openuidev/react-ui build succeeds
• dist/openui-defaults.css contains :root { --openui-*: ... }
• dist/components/index.css starts with :root block
• Individual component CSS uses bare var() without fallbacks
• dist/styles/openui-defaults.css exists and is importable
• Storybook renders correctly (ThemeProvider injects all vars at runtime)

🤖 Generated with Claude Code