Publish versioned sample Runtime images for v0.1

[XnLemon]

Closes #15

Outcome

• keep both independent Runtime implementations on stable Agent ingress /agent/v1
• pin the exact Core and SDK v1 candidates
• publish Runtime A and Runtime B as multi-architecture GHCR images from annotated semantic tags
• attach exact source commits, immutable image digests, OCI provenance/SBOM attestations, and checksums to the release

Validation

• go mod tidy
• go build ./...
• go test ./...
• go test -race ./...
• go vet ./...
• workflow YAML parse

Local Docker was unavailable; both image builds and the two-runtime live loop remain required CI/Stack gates.