[housekeeping] upgrade tailwindcss from v3 to v4

[Yonava]

Key Benefits of Upgrading to Tailwind v4

• Massive Performance Gains: Powered by a new Rust engine, cutting production build times by up to 5x and delivering near-instantaneous local HMR.
• Eliminates Configuration Boilerplate: Wipes out postcss.config.js and tailwind.config.js entirely, shifting configuration to a unified, CSS-first @theme syntax.
• Built-in Lightning CSS Integration: Drops external dependencies like autoprefixer and postcss-import by natively handling vendor prefixing, minification, and CSS nesting.
• Automatic Content Scanning: Removes the error-prone content glob array; Tailwind now automatically maps our monorepo dependency graph to find utility classes.
• Native CSS Variables: Theme values automatically compile to standard CSS Custom Properties (e.g., var(--color-*)), allowing seamless sharing between utility classes and global stylesheets with zero runtime overhead.