feat: Add GitHub Packages publishing alongside NuGet.org

[petre-c]

Summary

• ✅ Added dual package publishing to both NuGet.org and GitHub Packages
• ✅ Fixed release workflow to trigger on GitHub release events
• ✅ Split publishing into separate targets for flexibility

How It Works

When you create a GitHub Release:

1. The release workflow automatically triggers
2. Nuke builds and creates NuGet packages
3. Packages are published to:
   • NuGet.org - Public distribution (requires NUGET_API_KEY secret)
   • GitHub Packages - Private/internal use (uses automatic GITHUB_TOKEN)

Changes Made

Nuke Build Updates

• Created PublishToNuGet target for NuGet.org
• Created PublishToGitHub target for GitHub Packages
• Publish target now triggers both
• GitHub Packages uses the automatic GITHUB_TOKEN

Workflow Fixes

• Release workflow now triggers on release: published events
• Manual workflow_dispatch trigger still available for testing

Package Locations

• NuGet.org: https://www.nuget.org/packages/AppifySheets.TBC.IntegrationService.Client
• GitHub Packages: https://github.com/AppifySheets/TBC-IntegrationService-StandardPlus-Client/packages

Test Plan

• Nuke build compiles successfully
• Version check passes (1.0.1)
• Release workflow will trigger on GitHub release
• Packages will publish to both registries

Collaboration by Claude