docs: document the provider option and refresh the vendor list in chat()

[meridah7]

What

Two documentation changes to puter.ai.chat():

1. Document the provider option, which is not currently in the options list.
2. Refresh the vendor list, which names 7 vendors while puter.ai.listModelProviders() returns 16.

Why

provider is undocumented. ChatCompletionDriver.complete() reads args.provider and passes it to #resolveModel() to pin a request to a vendor, and puter.ai.chat() forwards the option through. Nothing in the docs mentions it, so there is currently no documented way to ask for a specific vendor.

The vendor list is stale. Both places name OpenAI, Anthropic, Google, xAI, Mistral, OpenRouter and DeepSeek. puter.ai.listModelProviders() returned 16 ids when I ran the playground example on 2026-08-04:

alibaba, azure-openai, azure-openai-responses, claude, deepseek, gemini, infron,
minimax, mistral, moonshotai, openai-completion, openai-responses, openrouter,
together-ai, xai, zai

The replacement list is those ids written as company names, merging the two pairs that are one vendor (azure-openai + azure-openai-responses, openai-completion + openai-responses). It is the API response rather than a hand-picked selection.

Both new links also give listModelProviders its first inbound link from the docs. Nothing currently links to that page.

One question for a maintainer

I deliberately did not document what happens when the requested vendor does not serve the requested model. #resolveModel() currently returns models.find(m => m.provider === provider) ?? models[0], so it falls back to the default vendor for that model rather than erroring. I did not want to write that down as intended behaviour without someone confirming it is intended. Happy to add a sentence either way, or to leave it out.

Disclosure

Infron is one of the vendors added to the list. I work on the Infron provider integration merged in #3433. The list is taken from the API response rather than curated, and the provider documentation applies to every vendor equally.