Refresh first-class model allowlists

[antonvishal]

why

The allowlists still named retired OpenAI, Anthropic, and Google IDs. Docs and fixtures were pointing at the same stale names.

what changed

Protocol allowlists now keep IDs that are still on the provider APIs. Python generated models, v4 docs, and SDK/extension fixtures follow. Eval defaults were left alone so older runs stay comparable.

test plan

• just generate (protocol JSON, Python models, Go client, extension zip)
• just fmt
• just check (fmt, lint, typecheck, Python generate --check, ruff, ty, Go generate --check, gofmt, go vet)
• just test
  • turbo unit/browser: 33/33 packages
  • Python: 529 passed, 1 skipped
  • Go: sdk-go, extensionassets, extensionpack, generator

---

Summary by cubic

Refreshes the first-class model allowlists to keep only IDs that are still reachable on the OpenAI, Anthropic, and Google APIs, and updates docs, generated SDKs, and fixtures to use current model names.

• Removes retired model IDs from the protocol allowlists; those IDs now fail model validation.
• Adds currently available IDs such as openai/gpt-6-astra, anthropic/claude-sonnet-5, and google/gemini-3.8-flash.
• Updates v4 docs, generated Python and Go models, the extension zip, SDK tests, and the eve README to the new model names.
• Bumps the inferred Google default from google/gemini-3.6-flash to google/gemini-3.8-flash.
• Leaves eval defaults untouched so historical runs stay comparable.

^{Written for commit d063084. Summary will update on new commits.}

[changeset-bot]

⚠️ No Changeset found

Latest commit: d063084

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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.