Update AI model code gen to convert markdown to C# XML docs

[JamesNK]

Description

Fixes #13543

Read description as markdown and convert to C# XML docs.
I haven't regenerated output files in the repo.

Example:

Checklist

• Is this feature complete?
  • Yes. Ready to ship.
  • No. Follow-up changes expected.
• Are you including unit tests for the changes and scenario tests if relevant?
  • Yes
  • No
• Did you add public API?
  • Yes
    • If yes, did you have an API Review for it?
      • Yes
      • No
    • Did you add <remarks /> and <code /> elements on your triple slash comments?
      • Yes
      • No
  • No
• Does the change make any security assumptions or guarantees?
  • Yes
    • If yes, have you done a threat model and had a security review?
      • Yes
      • No
  • No
• Does the change require an update in our Aspire docs?
  • Yes
    • Link to aspire-docs issue (consider using one of the following templates):
      • New (or update) doc-idea template
      • New breaking-change template
      • New diagnostic template
  • No

[github-actions]

🚀 Dogfood this PR with:

⚠️ WARNING: Do not do this without first carefully reviewing the code of this PR to satisfy yourself it is safe.

curl -fsSL https://raw.githubusercontent.com/dotnet/aspire/main/eng/scripts/get-aspire-cli-pr.sh | bash -s -- 13548

Or

• Run remotely in PowerShell:

iex "& { $(irm https://raw.githubusercontent.com/dotnet/aspire/main/eng/scripts/get-aspire-cli-pr.ps1) } 13548"

[Copilot]

Pull request overview

This PR enhances the AI model code generator to convert markdown descriptions from the Azure AI Foundry model catalog into properly formatted C# XML documentation comments. Instead of simply escaping and inserting text, it now parses markdown and converts it to appropriate XML doc tags (like <para>, <list>, <c>, <b>, <see>, etc.).

Key changes:

• Adds Markdig dependency for markdown parsing
• Implements comprehensive markdown-to-XML conversion supporting paragraphs, headings, lists, code blocks, emphasis, links, and line breaks
• Improves description cleaning to handle BOM characters and use culture-aware string replacements