Per gstack team-mode install: adds a PreToolUse hook that blocks
skill usage when gstack isn't installed globally, so contributors
are prompted to install it. Un-ignores the two required files
(.claude/settings.json, .claude/hooks/check-gstack.sh) while
keeping settings.local.json and other Claude state ignored.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
