Publish @arcp/* packages to npm

[nficano]

All five packages (@arcp/sdk, @arcp/client, @arcp/core, @arcp/runtime, @arcp/middleware-*) are at 0.1.0 locally and npm view @arcp/sdk version returns E404 — they are not on the registry.

Steps:

1. Bump versions per CHANGELOG.md if not already
2. Confirm .github/workflows/publish.yml is fixed (see related issue) — it should be the publish path
3. Tag a release: gh release create v0.1.0 --generate-notes (or chosen version)
4. Verify each package lands: npm view @arcp/sdk @arcp/client @arcp/core @arcp/runtime version
5. Update README install snippet if needed

The TS SDK is the reference implementation; an unpublished reference makes downstream SDKs harder to consume.

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