Fixes #13: CSS performance optimizations
- Add CSS minification support to build script (--minify flag)
- Pure JS minifier: removes comments, whitespace, redundant chars
- Reports size reduction percentage
- Preserves CSS custom properties, data URIs, strings
- Refactor _08_themes.css: extend CSS custom properties pattern
- Define theme-specific properties per theme (--rpg-content-bg,
--rpg-content-box-shadow, --rpg-header-text-shadow, etc.)
- Replace triple-theme selector duplication with single [data-theme]
selectors — children inherit variables automatically
- Reduces themes.css from 379 to ~220 lines
- Reduces style.css from 305KB to 294KB (3.8% reduction)
- Add build:css:min npm script for production builds
- Add 9 tests for CSS build: minification, size reduction, CSS
variable preservation, data URI preservation, theme refactoring
ARIA
df7d3b3a38