Fix `postinstall` script failure on Windows (cross-platform compatibility)

[md-shoaib-alam]

Describe the Bug

When running npm install on Windows, the installation fails during the postinstall lifecycle hook.

The current postinstall script relies on POSIX/bash-specific syntax ([ and || true), which is not recognized by the default Windows Command Prompt (cmd.exe).

Error Log

> openwa@0.1.6 postinstall
> [ -d dashboard ] && npm run dashboard:install || true

'[' is not recognized as an internal or external command,
operable program or batch file.
'true' is not recognized as an internal or external command,
operable program or batch file.
npm error code 1

[md-shoaib-alam]

The Solution (Applied Fix)
We can resolve this issue by replacing the POSIX/bash-specific syntax with a native Node.js inline command. Since Node.js is guaranteed to be present when running npm, this method works seamlessly across Windows, macOS, and Linux without requiring any third-party packages.

🔄 Code Changes in package.json

- "postinstall": "[ -d dashboard ] && npm run dashboard:install || true",
+ "postinstall": "node -e \"if (require('fs').existsSync('dashboard')) { require('child_process').execSync('npm run dashboard:install', { stdio: 'inherit' }); }\"",