Add a warning at /warp boss (PVP enabled)

There is a safe area at /warp boss, but it's not marked where it is, nor is there any indication that PVP is enabled outside of it. It would be good to add a red line as an indicator, and perhaps also a hologram. It could say something along the lines of "PVP enabled in boss arena when there is no active fight, PVP disabled in boss arena during the fight".