Terrain feel: biome regions ~10x larger (Voronoi cell size 96->960); terrain height now eases across biome borders via a Voronoi distance blend (smooth, and ~25x cheaper than the old 169-sample box blur); mountains capped to ~2/3 world height and gentled (ridged amplitude/frequency lowered), snow line lowered to match.
Centralization: ~27 world-gen/render tuning constants (biome amplitudes & frequencies, climate-noise frequencies/octaves, biome-selection thresholds, blend width, cell size, filler depth, snow line, camera near plane, spawn offset, overlay scale) hoisted from scattered literals into a region-organized, fully-commented Configuration. Configuration is threaded into NoiseSource, the biomes, BiomeRegistry, BiomeMap (+Classify), TerrainSampler, WorldGenerator (+BlockAt filler depth), and Camera via Player. Defaults equal the prior values, so generation is unchanged; worldgen tests updated for the new constructor signatures.
Adds Configuration.VerticalPriorityWeight (default 4). The priority
formula in ChunkStreamer.RecomputeTargetSet now uses
dx^2 + dz^2 + dy^2 * VerticalPriorityWeight, so horizontal chunks at
the player's Y are dispatched before equally-distant chunks above or
below. Fixes janky loading where deep-underground chunks were
competing with surface chunks for early dispatch slots.
