Setup guides have invalid models and instructions that don't work for Pro users

Following the instructions in the following files:

https://github.com/anthropics/claude-code-action/blob/main/docs/setup.md
https://github.com/anthropics/claude-code-action/blob/main/docs/usage.md

Pro users can not actually use the actions as written due to two issues:

1. Claude Code Action defaults to Opus, but the token generated from `claude setup-token` is not allowed for Opus use. So when the action runs, you instead get a confusing 400 error from the API with the message `This credential is only authorized for use with Claude Code and cannot be used for other API requests`. It turns out, it's because it's trying to call Opus instead of Sonnet.
2. Following the instructions in the Usage file, however, lists a model that doesn't exist - `claude-4-0-sonnet-20250805` isn't a valid model, so the action will 400. It instead needs to be `claude-sonnet-4-20250514`.

I believe this is mostly a documentation issue for the manual setup paths.

Thank you!