uv tool install graphifyy runs graphify in an isolated venv, so when a backend
needs anthropic/openai/boto3 the old 'Run: pip install anthropic' advice never
reached it. Worse, claude was the only backend with no [extra] at all, so a user
with ANTHROPIC_API_KEY set could not satisfy it without --with anthropic.
Add an anthropic optional extra (and include it in [all]), and replace the
package-missing ImportError messages with a shared _backend_pkg_hint that points
at 'uv tool install graphifyy[<extra>] --force' first, then the pip/venv path.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Safi