feat: Implement portable PowerShell proxy for Ask Sage

[mark-e-deyoung]

Implemented a portable PowerShell version of the Ask Sage OpenAI proxy.

• Created powershell/AskSageProxy.ps1: The main proxy script using HttpListener and HttpClient.
• Created powershell/SampleUsage.ps1: A sample script demonstrating how to run and query the proxy.
• Updated README.md to include instructions for the PowerShell version.
• Ensured compatibility with Windows PowerShell 5.1 and PowerShell Core.
• Implemented custom multipart/form-data parsing to handle file uploads without external dependencies.
• Added debug logging via -Debug switch.
• Verified functionality with local test scripts.

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PR created automatically by Jules for task 13684698734172429249 started by @mark-e-deyoung

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[github-actions]

Thanks for the PR. This project is invite-only and only accepts PRs from approved collaborators.

[github-actions]

This repository is invite-only. Pull requests from unapproved actors or forks are automatically closed.

[mark-e-deyoung]

Closing for now. This adds a large new PowerShell server implementation and multipart parser without corresponding test coverage; we should revisit as smaller, test-backed changes if we prioritize PowerShell support.