Context

Issue #402 includes support for xAI's grok-build-0.1 coding model. This part is independent from OAuth and can land as a small API-key provider improvement.

The current xAI provider already uses the xAI Responses API in src/api/providers/xai.ts, and model metadata lives in packages/types/src/providers/xai.ts. Official xAI docs list grok-build-0.1 as the coding model, with grok-code-fast-1 as an alias/related model.

Developer Notes

• Add grok-build-0.1 to packages/types/src/providers/xai.ts with appropriate context, max output, tool preferences, and pricing metadata.
• Keep existing xai API-key behavior unchanged.
• Include search_replace and exclude apply_diff, matching existing xAI model patterns unless current model docs require otherwise.
• Add focused tests for model selection/default fallback where applicable.
• Do not include OAuth, web search, or X search behavior in this sub-issue.