Feat: Implement governance approval workflow

[rian-be]

Summary

Add governance approval workflow support on top of the existing request lifecycle and version resolution runtime.

Added

• Request level approval requirements and approval workflow runtime services
• Approval specific exceptions, models, and mapping from policy requirements
• Runnable governance approval workflow example
• Governance decision taxonomy example covering lifecycle, approval, and version resolution decisions

Changed

• Governance abstractions, runtime, and tests now use folder aligned namespaces
• Governance structure and example references are aligned across README files and solution entries
• Release publishing workflows now propagate the draft release version into package publishing

Result

Governance now supports explicit approval driven request progression with typed approval actions, updated examples, and consistent namespace/layout model across the package.

Testing

• dotnet build src/ModularityKit.Mutator.Governance.csproj -c Release
• dotnet test Tests/ModularityKit.Mutator.Governance.Tests/ModularityKit.Mutator.Governance.Tests.csproj -c Release

Linked Issues

• Closes [Task]: Implement governance approval workflow #7 - [Task]: Implement governance approval workflow

Checklist

• Approval workflow implemented in governance runtime
• Governance examples updated
• Governance tests updated and passing
• Release workflow version propagation adjusted