Re-add ghost space transitions, add ghost z level registering

code/modules/mob/dead/dead.dm

@@ -1,4 +1,33 @@
+/mob/dead/Login()
+	. = ..()
+	var/turf/T = get_turf(src)
+	if (isturf(T))
+		update_z(T.z)
+
+/mob/dead/Logout()
+	update_z(null)
+	return ..()
+
 /mob/dead/forceMove(atom/destination)
+	var/turf/old_turf = get_turf(src)
+	var/turf/new_turf = get_turf(destination)
+	if (old_turf?.z != new_turf?.z)
+		onTransitZ(old_turf?.z, new_turf?.z)
 	var/oldloc = loc
 	loc = destination
-	Moved(oldloc, NONE, TRUE)
+	Moved(oldloc, NONE, TRUE)
+
+/mob/dead/onTransitZ(old_z,new_z)
+	..()
+	update_z(new_z)
+
+/mob/dead/proc/update_z(new_z) // 1+ to register, null to unregister
+	if (registered_z != new_z)
+		if (registered_z)
+			SSmobs.dead_players_by_zlevel[registered_z] -= src
+		if (client)
+			if (new_z)
+				SSmobs.dead_players_by_zlevel[new_z] += src
+			registered_z = new_z
+		else
+			registered_z = null