🤖 Release: CI/CD workflow for 1.0.0-beta.1

[jongalloway]

Automate build/test/pack/publish for 1.0.0-beta.1.

Scope

• Build and test on pushes/PRs to main and tags.
• Pack NuGet(s) (symbols + SourceLink), publish to GitHub Packages or NuGet (dry-run acceptable pre-tag).
• Build and push demo container to GHCR with version tags.

Tasks

• GitHub Actions: dotnet setup, restore, build, test, pack
• Artifact upload: nupkg/snupkg and container image metadata
• Release job: on tag v1.0.0-beta.1 to push NuGet and GHCR
• Minimal caching and matrix for OS if useful

Acceptance Criteria

• Green pipeline generates artifacts
• Tagging v1.0.0-beta.1 publishes packages and images

Parent: #76