docs: refresh model names and recommendations

[antonvishal]

Summary

Refreshes model references across v4 documentation to current available model names and recommendations.

Part of breaking up #2920 into 3 PRs as requested in #2920 (comment) (docs).

• Updates model configuration guides and snippets to use active OpenAI, Anthropic, and Google model IDs.
• Updates model recommendations in v4 documentation following Browserbase Benchmark v2.

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Summary by cubic

Refreshes v4 docs to replace outdated model IDs with current model names and align recommendations with Browserbase Benchmark v2.

Docs-only change; no SDK behavior or configuration format changes. Old IDs like google/gemini-2.5-flash, anthropic/claude-sonnet-4-6, and openai/gpt-5.4-mini are replaced with current names across all examples. The quick reference in models.mdx now recommends OpenAI models for production, speed, and cost.

^{Written for commit 29cef2d. Summary will update on new commits.}

[changeset-bot]

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Latest commit: 29cef2d

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[github-actions]

This PR is from an external contributor and must be approved by a stagehand team member with write access before CI can run.
Approving the latest commit mirrors it into an internal PR owned by the approver.
If new commits are pushed later, the internal PR stays open but is marked stale until someone approves the latest external commit and refreshes it.

[antonvishal]

@miguelg719 The docs CI failure doesn’t look related to this PR. The existing Stainless OpenAPI URL in docs.json is returning a 404, and upstream/main fails the same validation locally.

Could you restore the published Stainless spec or update docs.json to point to the current URL?

[github-actions]

This PR was approved by @miguelg719 and mirrored to #2944. All further discussion should happen on that PR.

[github-actions]

The mirrored PR #2944 has been merged into main. This original external contributor PR will stay closed as completed.