Drops the manual mktemp + git-clone-with-token dance (not needed for a
public repo) in favor of actions/checkout@v4. GITEA_TOKEN is still
required for the release-creation and asset-upload API calls.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
.slnx requires .NET 9 SDK / MSBuild 17.8+. The Gitea runner has only
.NET 8, so build the test project directly — its ProjectReference
transitively builds ClaudeMailbox.csproj.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>