Add per-action test suites (baseline before consolidation)

[Marius Storhaug (MariusStorhaug)]

Summary

Wires each folded action''s own tests into PSMA CI, so we have a green baseline before the script consolidation (step 5). Replaces the template''s placeholder greeting test in Action-Test.yml with one job per action, each keeping the test approach it used as a standalone repo — adapted to its subfolder (uses: ./<Action>, test/scenario/fixture paths prefixed).

Jobs

• Resolve-PSModuleVersion — Pester suite via Invoke-Pester on ./Resolve-PSModuleVersion/tests (the 188-test version logic; the main safety net for step 5).
• Install-PSModuleHelpers — installs the action, verifies the Helpers module, runs its two regression scripts.
• Get-PSModuleSettings — valid + invalid (expect-failure) scenario invocations.
• Test-PSModule — Src-Default, Src-WithManifest, and outputs fixtures across Linux/macOS/Windows.

The 5 actions with no unit tests (Build/Document/Publish/Get-PesterCodeCoverage/Get-PesterTestResults) remain covered by the end-to-end pipeline (proven green via MariusTestModule).

Once this is green, step 5 (shared PSMA module + main.ps1 dispatcher) refactors under a passing suite. Tracking: PSModule/Process-PSModule#384 · closes the "colocated tests" goal of #347.