test: complete PowerShell v0.3 design corpus

[Aaronontheweb]

Summary

• promote 29 landed stable PowerShell design inputs into exact executable corpus entries
• add direct generated coverage for Measure-Command, Trace-Command, and valid ForEach-Object -RemainingScripts execution regions
• preserve authored sibling indices when the corpus generator projects multiple execution-region bodies
• record 84/90 PowerShell design cases as landed without claiming four deferred cases or the two remaining production gaps

The two stable cases still pending implementation are bounded-loop dynamic invocation and invalid local Invoke-Command -AsJob parameter-set rejection.

Verification

• dotnet build -c Release --no-restore
• dotnet test -c Release --no-build — 2,864 passed
• focused corpus/design/PII/PowerShell-oracle suite — 856 passed
• native PowerShell 7.6.4 execution of the RemainingScripts case
• slopwatch analyze --no-baseline --fail-on warning — 0 findings
• pwsh ./scripts/Add-FileHeaders.ps1 -Verify
• openspec validate --all --strict — 4 passed
• adversarial review — PASS after correcting the invalid first RemainingScripts example