fix(build): make react-ui and browser-bundle build scripts cross-plat…

[shogun444]

What

Fixes #603 by replacing Unix-specific build commands with cross-platform Node.js helper scripts in @openuidev/react-ui and @openuidev/browser-bundle.

On Windows, builds fail with:

'rm' is not recognized as an internal or external command,
operable program or batch file.

Changes

Replaced rm -rf and mkdir -p usage with Node.js filesystem APIs while preserving the existing build behavior.

Test Plan

• Not applicable (explain why)
• Verified locally

Validated on Windows 11 using PowerShell.

@openuidev/react-ui now builds successfully.

@openuidev/browser-bundle progresses past the shell-command failure and reaches the bundling stage. Validation exposed a separate module resolution issue:

Could not resolve "./openuiLibrary.tsx"
Could not resolve "./library.ts"
Could not resolve "./Renderer.tsx"

These errors appear unrelated to the Windows compatibility issue addressed in this PR.

Checklist

• I linked a related issue, if applicable
• I updated docs/README when needed
• I considered backwards compatibility