Every skill now runs bin/gstack-update-check on invocation. If an upgrade
is available, reads gstack-upgrade/SKILL.md inline upgrade flow.
Also adds AskUserQuestion to 5 skills that lacked it (gstack root, browse,
qa, retro, setup-browser-cookies) and Bash to plan-eng-review.
Simplifies qa and setup-browser-cookies setup blocks (removes META parsing).