feat(ci): use new gominimal/check action - #735

Resolve the conflicts from the commits that landed on main since this
branch's merge-base (#721, #732, #734, #735, #722), keeping main's
content and re-applying the `min` binary-target rename on top.

- justfile: main folded `up` into `dm1` (#722), so the branch's older
  `up` recipe is dropped rather than resurrected. Main's `dm1` invoked
  the `{{minimal}}` variable this branch renames, which would have left
  `just` unable to resolve it; it now invokes `{{min-bin}}`.
- CI lanes: keep main's rewritten jobs and steps, renaming only the CLI
  build flags and built-binary paths (`--bin min`, `target/debug/min`).

Also point the sessions example project at `./target/debug/min`; the
binary path it documented no longer exists after the rename.

Published release asset names (`minimal-linux-amd64`, ...), the macOS
`minimal` shim, and the `minimal` crate and lib target are deliberately
left alone.