First tagged release of the reference registry server.

Highlights

• Optional read/write Bearer auth (REGISTRY_READ_TOKEN, REGISTRY_WRITE_TOKEN)
• Rate limiting, structured logs, optional Prometheus /metrics
• GET /readyz, GET /version, registry -version (stamp with -ldflags)
• CI: go test, gofmt, e2e-smoke with skillget + private module auth
• SECURITY.md, public runbook

Build

go build -ldflags "-X github.com/getskillpack/registry.Version=v0.1.0" -o registry ./cmd/registry

See README and docs/PUBLIC_REGISTRY_RUNBOOK.md.