docs(DEV): Improve Windows Instructions for GitHub Packages PAT

[saishmungase]

Problem

Windows users encounter 401 Unauthorized errors when installing dependencies because the Developer Guide only documents Linux/macOS .npmrc setup.
The missing part is the registry scope entry for @sugarlabs, which Windows users must manually configure.

Solution

This PR adds a dedicated Windows (PowerShell) section with the correct .npmrc configuration, ensuring both:
the @sugarlabs registry is set
the GitHub PAT is applied properly

Added Instruction

Set-Content $env:USERPROFILE\.npmrc "@sugarlabs:registry=https://npm.pkg.github.com`n//npm.pkg.github.com/:_authToken=YOUR_GITHUB_ACCESS_TOKEN"

Fixes #472