CLAUDE.md: a release contains everything on main when it is tagged

A new bullet, placed right after the existing release rule about the README:

- Every release also brings the README's text up to date: like the site, it names what the release
  adds that a newcomer should know (phone remote control, say).
+ A release contains everything on `main` at the moment it is tagged: right before tagging, rebase
+   onto the current `main` (moving the tag if it is already set), so commits that landed while the
+   release was being prepared go into it too.
- gh calls against this repository's GitHub repository go through `bun scripts/gh.ts <gh args…>`: …