feat(ci): path detector + Invoke-GoTest wrapper (#562 2/4)

[WilliamBerryiii]

Part 2 of 4 splitting #562 into reviewable PRs.

Parent: #562
Depends on: #567

Scope

Add the changed-folder detector field and the PowerShell wrapper invoked by npm run go-test. No workflow yet consumes the new detector field, so this PR adds no required CI gate.

Files

• scripts/build/Detect-Folder-Changes.ps1 — emit new goContractTests JSON field.
• scripts/build/Detect-Folder-Changes.Tests.ps1 — Pester coverage for the new field.
• scripts/linting/Invoke-GoTest.ps1 — wrapper that runs go test against changed blueprint test directories.
• scripts/tests/linting/Invoke-GoTest.Tests.ps1 — Pester coverage for the wrapper.
• package.json — add go-test npm script targeting the wrapper.

Acceptance criteria

• pwsh ./scripts/Invoke-Pester.ps1 -CI -Path ./scripts/build/Detect-Folder-Changes.Tests.ps1 passes (expect 27/0/0).
• pwsh ./scripts/Invoke-Pester.ps1 -CI -Path ./scripts/tests/linting/Invoke-GoTest.Tests.ps1 passes (expect 14/0/0).
• npm run go-test with no changes to gated paths exits cleanly (skip behavior).
• Detector emits the new goContractTests field but no workflow yet consumes it.