Feat: Improve governance DX and docs

[rian-be]

Summary

This PR improves governance API ergonomics and restructures the API documentation into a clearer package oriented layout. It reduces call site noise in governance flows, updates the examples to use the shorter patterns, and adds dedicated API guides for governance and Redis.

Added

• category specific MutationRequestDecision helpers for lifecycle, approval, and version-resolution decisions
• IVersionedState execution overload for IGovernanceExecutionManager.ExecuteApproved(...)
• dedicated Docs/API/ folder with separate governance, Redis, and core API reference documents
• focused tests covering the new MutationRequestDecision helper methods

Changed

• governance request factories now use the category specific decision helpers internally
• governance runtime execution, approval, and version resolution paths now use the shorter decision APIs
• governance examples now demonstrate the simplified DX patterns
• governance and Redis package READMEs now point to the dedicated API docs

Result

The governance surface is now shorter and more consistent at the call site. Common operations such as request creation, decision recording, and approved execution require less boilerplate, and the documentation now separates core, governance, and Redis usage more clearly.

Testing

• verified dotnet test Tests/ModularityKit.Mutator.Governance.Tests/ModularityKit.Mutator.Governance.Tests.csproj
• verified dotnet build Examples/Governance/GovernedExecution/GovernedExecution.csproj
• verified dotnet build Examples/Governance/Queries/Queries.csproj
• verified dotnet build Examples/Governance/RedisQueries/RedisQueries.csproj
• verified dotnet build Examples/Governance/DecisionTaxonomy/DecisionTaxonomy.csproj

Checklist

• governance decision creation has dedicated DX helpers
• approved execution supports the IVersionedState shortcut overload
• governance examples are updated to use the shorter API surface
• API documentation is split into dedicated core, governance, and Redis guides