Serialises Mob.Theme's native probes: each probe runs inside this locally registered process, one at a time, so concurrent first theme calls share one mob_nif load attempt instead of each retrying it.

Not :global.trans/3: it backs off by sleeping under contention, which stalls concurrent first theme calls on render paths, and it releases on the node name captured at acquire time, so Mob.Dist starting distribution during a probe leaves the lock held for good and every later probe blocks (MOB-311). Started on first use and unlinked, like Mob.DNS.Seeder, because mob has no supervision tree of its own.