Support different project / config location paths

[daaain]

I found out from ccusage's docs that Claude Code can store its config and sessions in multiple directories depending on the version.

It's an utter mess though, the change was shipped and unshipped.

There are lots if issues in their Github, this one has a bit more convo / info.

Ultimately, we might also need to support XDG: anthropics/claude-code#2350

This PR is a good starting point for implementation.

[cboos]

Don't we have --projects-dir now, for the unconventional cases?

[daaain]

We do for manual workaround, but it would be nice to auto-detect.

Not urgent, but once CC changes the default directory permanently, more and more people will have the issue.