Send OpenRouter app-attribution headers

[DevMortimer]

Wanted

Send OpenRouter's app-attribution headers on the OpenRouter backend (docs):

• HTTP-Referer: required for an app page and for rankings.
• X-OpenRouter-Title: the display name.
• X-OpenRouter-Categories: for example cli-agent or ide-extension.
• Optionally X-OpenRouter-App-Visibility: hidden.

By default, name pi-typesafe. Add a createTypeSafe option (for example attribution) so an extension built on this library can name itself instead.

Constraints

• The headers go only to the OpenRouter backend. Requests to the TypeSafe backend stay exactly as they are.
• The headers carry no secret and no user content.
• The SDK client accepts defaultHeaders. Check that they reach the injected fetch on both the judgment request and the model list.