M1: Add Invoke-HelpGenerator cmdlet to generate MAML from a module path

[jeffpatton1971]

Create a cmdlet that wires together:

ModulePath → Parse → Canonical model → Render MAML → Validate → Write files

Proposed signature

• Invoke-HelpGenerator -ModulePath <path> -OutputPath <path> [-Culture en-US] [-Force]

Definition of done

• Cmdlet is exported by HelpGenerator.Powershell.
• Returns a simple result object (paths written, counts) or writes verbose messages (your preference).
• Handles errors with actionable messages (schema failures included).

Acceptance checks

• Integration test executes cmdlet and validates files exist + validate step ran.