Fix approved required-module publish validation

[PrzemyslawKlys]

Summary

• Make repository publish dependency validation trust the final module manifest when it exists, including when RequiredModules is empty.
• Add regression coverage for a module configured as both required and approved so approved/merged modules do not reappear during publish validation.
• Keep the missing-manifest fallback to the planned required modules for defensive scenarios.

Root cause

Publish validation only used the final manifest when it contained at least one RequiredModules entry. When approved-module merge removed the last dependency from the manifest, validation fell back to the unfiltered plan and checked the dependency against PSGallery anyway.

Validation

• dotnet test .\PowerForge.Tests\PowerForge.Tests.csproj -c Release --filter "FullyQualifiedName~ModulePublisherRequiredModulesTests|FullyQualifiedName~ModulePipelineApprovedModulesTests|FullyQualifiedName~RequiredModuleResolutionEngineTests"