feat: add dense fog westeros event

[alecejones]

Currently the event doesn't work - had issues identifying where to call updateVisibleRegions with userVisibility = 0. If I could get assistance on that, it will work. Movement does not reveal enemies in fogged regions until moves are confirmed, so people can 'wander into an ambush'. You can detect that denseFog is in play with planningRestrictions, but there may be a better way to do this.

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