[czj]

AGENTS.md said how to release, but not what a release asks of the person running it, nor how to tell that another session had just released: two sessions working on one gem ended up unsure whether a version was out.

This pull request rewrites the Releases section and tightens the rest of the file without dropping anything.

• Releases: the user is needed for a working git signing key and one click on the release environment; check for a release already under way first; --dry-run then --yes; bin/release --tag after an interruption; an unsigned tag is never released.
• Same shared sections: the rules, pull request and release sections stay word for word identical in super-slim, gamba, crumbly and agentry.
• Tighter wording: the other sections say the same in fewer words; the Releases section grows by the steps it lacked, so the file ends about 70 words longer.