fix(opencode): plugin/openai add GPT-5.6 family

[dalisoft]

Issue for this PR

Closes #36140, #36427

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

This PR adds new model names in models list

How did you verify your code works?

Currently can't test but it should work

Screenshots / recordings

If this is a UI change, please include a screenshot or recording.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

If you do not follow this template your PR will be automatically rejected.

[github-actions]

This PR doesn't fully meet our contributing guidelines and PR template.

What needs to be fixed:

• Not all checklist items are checked. Please confirm you have tested locally and have not included unrelated changes.

Please edit this PR description to address the above within 2 hours, or it will be automatically closed.

If you believe this was flagged incorrectly, please let a maintainer know.

[github-actions]

Hey! Your PR title fix(opencode/plugin/openai): add GPT-5.6 family doesn't follow conventional commit format.

Please update it to start with one of:

• feat: or feat(scope): new feature
• fix: or fix(scope): bug fix
• docs: or docs(scope): documentation changes
• chore: or chore(scope): maintenance tasks
• refactor: or refactor(scope): code refactoring
• test: or test(scope): adding or updating tests

Where scope is the package name (e.g., app, desktop, opencode).

See CONTRIBUTING.md for details.

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Found potential duplicates related to GPT-5.6 model support:

Related Open PRs:

1. #36143 - fix(opencode): support GPT-5.6 Responses Lite - Adds GPT-5.6 Responses Lite support to opencode
2. #36393 - fix(provider): expose GPT-5.6 max reasoning - Exposes max reasoning for GPT-5.6
3. #36320 - feat(llm): support GPT-5.6 prompt cache new options - Adds prompt cache support for GPT-5.6
4. #36248 - fix(openai): use codex context limits for gpt-5.6 - Sets context limits for GPT-5.6

Why they're related: These PRs are all adding GPT-5.6 family support to different subsystems (opencode core, provider, LLM, and OpenAI plugin). They appear to be part of a coordinated effort to add GPT-5.6 support across the codebase. Check if #36476 is consolidating or duplicating this work, particularly regarding the OpenAI plugin-specific parts.

[github-actions]

This pull request has been automatically closed because it was not updated to meet our contributing guidelines within the 2-hour window.

Feel free to open a new pull request that follows our guidelines.