Added mine buildings to the build menu. Mines reveal the resource regions beneath them using a MineMask with a darkened fill overlay that masks the fog-of-war over the mined area. The region reveal creates a nice exploration feel where you discover what resources are under each segment.

Switched the region generation algorithm to use Voronoi tessellation, which produces much more natural-looking resource distributions. Borders between adjacent regions of the same resource type are now hidden so contiguous deposits read as a single area. Extracted shared utilities like drawPolygonPath and regionEdges into their own modules.