Fix Windows build compatibility in package scripts

[CodexNexor]

Summary

• replace Unix-only template/dist cleanup commands with small Node-based scripts in openui-cli, react-ui, and browser-bundle
• fix packages/react-ui/cp-css.js to resolve import.meta.url with fileURLToPath, which works correctly on Windows paths
• keep existing build behavior intact on macOS/Linux while making the same flows work under Windows pnpm

Validation

• ran node packages/openui-cli/scripts/build-templates.mjs
• ran node packages/browser-bundle/scripts/prepare-dist.mjs
• ran node packages/react-ui/scripts/clean-dist.mjs

Closes #445.

[vishxrad]

Thanks a lot for your contribution! Since this issue is already closed and a pr has been merged, I will close this pr. I would appreciate it if you could take a look at the other open issues and work on them.