gstack-relink now checks if a skill directory is already named gstack-*
before prepending the prefix. Previously, setting skill_prefix=true would
create gstack-gstack-upgrade, breaking the /gstack-upgrade command.
Matches setup script behavior (setup:260) which already has this guard.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
New bin/gstack-relink creates prefixed (gstack-*) or flat symlinks
based on skill_prefix config. gstack-config auto-triggers relink
when skill_prefix changes. Setup guards against recursive calls
with GSTACK_SETUP_RUNNING env var.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>