Add GPT 5.6 agent model support

[shrisukhani]

Summary

Adds Node SDK model literals for the GPT-5.6 models introduced in browserctrl#1211, while limiting HyperAgent support to Luna.

Changes

• Add gpt-5.6-sol, gpt-5.6-terra, and gpt-5.6-luna to CuaLlm
• Add gpt-5.6-luna to HyperAgentLlm
• Bump the package version to 0.91.4

Validation

• yarn lint
• yarn build

Link to Devin session: https://app.devin.ai/sessions/f284337c4bc9449da73ead049ff14a40
Requested by: @shrisukhani

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Note

Low Risk
Additive TypeScript string-literal unions and a patch version bump only; no runtime or API client logic changes.

Overview
Extends the Node SDK type definitions so clients can pass GPT-5.6 model IDs when starting agent tasks, aligned with backend support from browserctrl#1211.

CUA (CuaLlm) now includes gpt-5.6-sol, gpt-5.6-terra, and gpt-5.6-luna (existing GPT-5.x entries are unchanged; the union is reformatted for readability). HyperAgent (HyperAgentLlm) adds only gpt-5.6-luna, so Sol/Terra are CUA-only in this SDK surface.

Package version is bumped to 0.91.4 for release.

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