Let same-repository remotes carry checkpoints past the sync gate

A clone with a GitHub remote and an Entire mirror of the same repository captured one of them as the checkpoint sync remote, so every push to the other held checkpoints back and printed "N checkpoint(s) are waiting to sync". Mirrors push through to GitHub and sync every ref back, so both remotes reach one repository and the gate had no audience to protect.

The gate now also admits a configured remote whose every push URL names the same known-forge repository as the elected remote's. Unknown hosts, SSH aliases, Entire-native repos, raw URL pushes, and multi-URL remotes that fan out to different repositories still fail the match. The election, capture, and read candidates are unchanged.