Adopt and maintain the apache-magpie framework in a project repo via the snapshot-based adoption mechanism. The only framework skill committed in an adopter's repo; every other skill is a symlink the adopt sub-action wires up. Sub-actions: `/magpie-setup` - first-time adoption (default; main-checkout only) `/magpie-setup upgrade` - refresh the gitignored snapshot per the committed lock (main-checkout only) `/magpie-setup worktree-init` - symlink a worktree's snapshot to the main's `/magpie-setup verify` - health check + drift detection `/magpie-setup skill-sources` - fetch/pin/symlink skills from trusted external sources listed in the adopter trust list (main-checkout only) `/magpie-setup override <skill>` - open or scaffold an agentic override in `.apache-magpie-overrides/` `/magpie-setup unadopt` - reverse the adoption (snapshot, locks, symlinks, hook, doc sections); preserves `.apache-magpie-overrides/` by default (main-checkout only)