Tag v1.1.0 and publish to pkg.go.dev

[nficano]

Repo has no git tags. Once milestone work (issues from M0–M18 series, if recreated) is complete and CI is green:

1. git tag v1.1.0
2. git push origin v1.1.0
3. gh release create v1.1.0 --generate-notes
4. Trigger pkg.go.dev indexing: curl https://proxy.golang.org/github.com/agentruntimecontrolprotocol/go-sdk/@v/v1.1.0.info
5. Verify at https://pkg.go.dev/github.com/agentruntimecontrolprotocol/go-sdk

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Audit reference: ARCP SDK Audit v1.1 (2026-05-19)