Add Gemini 3 Pro CUA support

[rgarcia]

Summary

• Add gemini-3-pro-preview to the @onkernel/cua-ai Google CUA model annotations.
• Document the model in the supported CUA models list.
• Cover the exact-id annotation in the model tests.

Validation

• npm run build --workspace @onkernel/cua-ai
• npx vitest run --api.host 127.0.0.1 (from packages/ai)
• Live smoke: google:gemini-3-pro-preview returned a batch_computer_actions click from a screenshot prompt

---

Note

Low Risk
Low risk: adds a new allowlisted Google model ID plus docs/tests, without changing request/response logic or provider integrations.

Overview
Adds Google CUA support for gemini-3-pro-preview by extending CUA_MODEL_ANNOTATIONS and documenting it in supported-models.md.

Updates models.test.ts to assert the new exact-ID annotation is recognized.

^{Reviewed by Cursor Bugbot for commit 9019e88. 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 modifies AI/CUA model annotations and tests, not kernel API endpoints or Temporal workflows as specified in the filter.

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