Cap anthropic dependency to <1 (#4864)

* Cap anthropic dependency to <1

The anthropic SDK is approaching a 1.0 release with breaking changes.
Add an upper bound so existing installs don't pick it up automatically.

No-Verification-Needed: dependency specifier change only

* Regenerate dependency lockfile

---------

Co-authored-by: Jeremiah Lowin <153965+jlowin@users.noreply.github.com>