fork.40 errored after 5s ("reload the extension"), which still pushed the problem
onto the user. Extend the relay-reconnect wait to ~15s when the extension is
installed: enough for the MV3 service worker to wake and reconnect on its own
(onStartup after a Chrome restart, or the keepalive alarm). The loop re-checks
the relay file each iteration, so a mid-wait recovery is picked up instantly and
the full window is only spent when the extension is genuinely down. End users no
longer have to do anything when the relay blips.