Kubo migration cannot stop an alpha.25 daemon that outlived Runtime (--enable-gc ignores API shutdown) #505

Found 29 Oct while testing the 0.8.0-alpha.26 candidate (8a74b66).

What happens: Kubo started with --enable-gc (every alpha.25 and alpha.26 daemon) answers /api/v0/shutdown with 200 but does not exit until a second interrupt. The offline migration (retire_online_coord, capsules/ipfs-provider) relies on that API shutdown, so if an alpha.25 online daemon is still running when the new Runtime starts, the migration refuses every start and local IPFS stays unusable until a reboot or a manual kill; the old daemon keeps running online.

Why it does not affect normal installs: the installed stop and elastos update kill Runtime's whole process group (update_controller/child.rs), which includes Kubo, so the old daemon is gone before the new Runtime starts. CI update journeys pass. It shows only when a daemon survives outside that, e.g. after a crash or on source Homes (scripts/mac-source-home-restart.sh signals only the gateway pid).

Fix (0.8.1): in retire_online_coord, after a daemon proven to be ours (our PeerID from /id, holds our repo lock) accepted /shutdown and is still alive after 5 s, send it one SIGTERM (Kubo's own second-interrupt force stop); keep the refusal if it still runs. Make the real-Kubo test start its online daemon with --enable-gc so it fails before the fix. Also have the source-Home restart script stop the gateway's process group.