Drop the bu-3 and bu-3-max model ids everywhere they were surfaced:
- ChatBrowserUse no longer lists them as valid bu-* aliases (provider-prefixed
ids like openai/gpt-5.5 are still accepted by the gateway).
- Remove their custom pricing entries and the README pricing blocks.
- Update docstrings, README quickstart, and the beta_agent example to use
openai/gpt-5.5 as the default, with bu-2-0 shown as a commented alternative.
- Drop the tests that asserted bu-3/bu-3-max acceptance and pricing.
ChatBrowserUse now accepts provider-prefixed model ids (anthropic/*,
openai/*, google/*) alongside the bu-* aliases and browser-use/* models,
so a single BROWSER_USE_API_KEY can reach them. bu-* aliases and the
bu-latest -> bu-2-0 normalization are unchanged; bare ids are rejected
with guidance toward the provider/model form.
Also matches provider-prefixed Claude Sonnet ids in the Agent
llm_screenshot_size auto-config, so the screenshot optimization isn't
lost when Claude is reached via ChatBrowserUse.
Adds an example, a README FAQ entry, and tests.
ENG-5060
Alexander Yue