Add option to skip installation steps if claude is already installed

[asvoboda]

In some self-hosted environments, it would be useful to avoid needing to pull in another dependency (like oven-sh/setup-bun) and run a bun install if the dependencies are already present.

Could the install steps be replaced in favour of either installing claude directly using npm, or even skip that step if the runner already has claude installed locally?

[asvoboda]

Specifically, I'm asking for something similar to checking if the relevant binaries are present in the tool cache and re-using that if possible to avoid making additional external requests

https://docs.github.com/en/enterprise-server@3.15/admin/managing-github-actions-for-your-enterprise/managing-access-to-actions-from-githubcom/setting-up-the-tool-cache-on-self-hosted-runners-without-internet-access

[asvoboda]

Resolved in #480 / #481