fix(ai): apply catalog settings to provider models - #39613

Summary

• make OpenRouter and xAI provider entrypoints implement the catalog provider-package contract
• apply credentials, base URLs, headers, body overlays, limits, and provider options
• add package contract coverage for both providers

Testing

• bun test test/provider-package.test.ts test/exports.test.ts (from packages/ai)
• git diff --check

Note

• bun typecheck is currently blocked by the workspace failing to resolve @standard-schema/spec from packages/schema/src/tool.ts