Migrate from Webpack to Vite

[devisnotnull]

• Replace Webpack 5 with Vite 5 for faster builds and HMR
• Add vite.config.ts for client build
• Add vite.config.server.ts for SSR server build
• Update package.json with Vite dependencies and ESM configuration
• Convert tsconfig.json to ESM module resolution
• Update postcss.config.js and tailwind.config.js to ESM
• Update server http.ts to read CSS from Vite manifest
• Update client entry to import CSS directly (Vite requirement)
• Fix CSS @import order for proper loading
• Add index.html as Vite entry point
• Update ESLint config for new JSX transform
• Update README with new build commands and documentation
• Remove Webpack and Babel dependencies (reduces deps by 61 packages)

Build output:

• Client: JS and CSS bundles in build/static/
• Server: SSR bundle as build/server.js

https://claude.ai/code/session_Cw06h

What has been done