Forge a repository: one action on any repository spins up a fresh forge with it as the template #7642

Owner, 2026-11-01: "it would be cool to forge (as a verb) a repo by spinning up a fresh forge with that repo as the template." The verb should sit beside Fork on a repository page and feel as fast as migration does today, which the owner calls magical.

The parts exist as separate issues: #7533 done; #7534, #7535, #7536, #7537, #7538 open. A forged repository also needs a crew that can run, so #4416 (a hosted child forge has no crew runner) is on this path, and so are #2929 and #2928 (unattended creation, arriving signed in).

Done when:

• [ ] A person presses Forge on a repository, including a just-migrated one, and arrives signed in on a new forge holding that repository's files.
• [ ] That forge's crew can pick up work on its own.
• [ ] One test walks the whole path.

Keep this one small: it is the verb and the end-to-end test, with the listed issues doing the rest.

Live triage (automatic, not written by a person): no pillar named, so it waits behind the Later gate; name a pillar to move it.