Clarify cua-ai runtime spec docs

[rgarcia]

Summary

• Rewrite CuaRuntimeSpec docs to describe the public runtime configuration use case.
• Remove package-internal framing around cua-agent and provider-neutral implementation details.

Tests

• npm test --workspace @onkernel/cua-ai
• npm run build --workspace @onkernel/cua-ai

---

Note

Low Risk
Doc-only updates to CuaRuntimeSpec/resolveCuaRuntimeSpec with no functional or behavioral changes, so risk is minimal.

Overview
Updates JSDoc in runtime-spec.ts to reposition CuaRuntimeSpec as a public runtime configuration object (model + tools + baseline prompt + optional payload middleware) and to clarify that resolveCuaRuntimeSpec returns provider defaults for building computer-use requests.

Removes package-internal references (e.g., cua-agent and provider-neutral implementation details) and tweaks field wording (e.g., toolDefinitions) without changing any runtime logic.

^{Reviewed by Cursor Bugbot for commit 3e1e7b9. Bugbot is set up for automated code reviews on this repo. Configure here.}

[firetiger-agent]

Firetiger deploy monitoring skipped

This PR didn't match the auto-monitor filter configured on your GitHub connection:

Any PR that changes the kernel API. Monitor changes to API endpoints (packages/api/cmd/api/) and Temporal workflows (packages/api/lib/temporal) in the kernel repo

Reason: PR only modifies documentation for the cua-ai package, not API endpoints or Temporal workflows.

To monitor this PR anyway, reply with @firetiger monitor this.