Add isolated module profile preflight validation

[PrzemyslawKlys]

Summary

• add reusable isolated module profile preflight validation in PowerForge.PowerShell
• add Test-IsolatedModuleProfile as a thin PowerShell cmdlet surface
• make Import-IsolatedModule fail before copy/import when a curated profile layout is invalid
• document source behavior in the authored module isolation doc and cmdlet XML comments; generated Module/Docs and help XML are left to the build pipeline

Validation

• dotnet build .\PSPublishModule\PSPublishModule.csproj -c Release
• dotnet test .\PowerForge.Tests\PowerForge.Tests.csproj -c Release --filter "ModuleIsolation|IsolatedModule"
• packaged-layout smoke import from temp Module/PSPublishModule.psd1: Test-IsolatedModuleProfile exported, MicrosoftGraphAuthentication preflight IsValid=True, IssueCount=0, PathCount=30