M1: Render canonical help model to MAML external help XML

[jeffpatton1971]

Convert the canonical model into MAML external help XML using System.Xml.Linq.

Definition of done

• Output matches a minimal valid MAML structure PowerShell expects for command help.

• Culture folder naming is supported (en-US default).

• Ordering is deterministic:

  • Commands sorted by Name
  • Parameters sorted by Position then Name (or Name if no Position)
  • Examples in source order

Acceptance checks

• Unit test snapshots the produced XML (string compare normalized).
• XML contains required sections for at least one command.