Night vision lighting

[Plateaus]

Added Night Vision spell as a timed personal visibility effect
Night Vision allows the affected player to see in dark rooms
Night Vision also allows directional looking into adjacent dark rooms
Updated directional LOOK to respect destination-room visibility
Light spell remains a shared light source for the caster's current room
Lit LIGHTABLE items now illuminate rooms
Dropped burning torches continue illuminating the room
Lit state is preserved as items move between inventory and rooms
Directional LOOK can see into an adjacent room illuminated by a dropped light source
Preserves distinction between personal vision effects and environmental light sources