Slightly tweaks and documents a do_after interaction (#23031)

Adds a new `do_after` flag for progress bar placement. Previously it was
placing the bar on `target` if it was provided in the arguments
(required by do_unique flags), with this flag we're now able to put the
bar on the user

This particular change fixes deployable kits not showing a progress bar.
Also documented some flags on the way

code/game/objects/structures/machinery/deployable.dm

@@ -271,7 +271,7 @@ Deployable Kits
 
 /obj/item/deployable_kit/attack_self(mob/user)
 	to_chat(user, SPAN_NOTICE("You start assembling \the [src]..."))
-	if(do_after(user, assembly_time, src, DO_REPAIR_CONSTRUCT))
+	if(do_after(user, assembly_time, src, DO_DEPLOY))
 		assemble_kit(user)
 		qdel(src)