Ports anthropics/skills#547 (b0cbd3d) so this repo matches the upstream
skills repo.
improve_description.py and run_loop.py now shell out to `claude -p` instead
of using the Anthropic SDK directly, so the description optimizer uses the
session's existing Claude Code auth and no longer requires a separate
ANTHROPIC_API_KEY. SKILL.md drops the stale extended-thinking reference and
adds guidance for updating an existing skill.
Several enterprise customers sync exclusively from this repo (not
anthropics/skills, whose README disclaims production use), so they have been
stuck on the old SDK-based path.
