Adds the species/organism layer on top of the gene foundation.
GenomeTemplate carries which GeneDefs an individual has plus the
per-organism base value and spread its alleles are drawn around (and an
optional discrete-variant override), so the same shared GeneDef expresses
different centres for different species — Generate() draws an individual,
Registry() feeds breeding and trait computation.
Genome.Breed gains an optional mutationChance that overrides every gene's
fixed MutationChance, so a caller can drive mutation from an evolvable
trait. Allele sampling (numeric spread+clamp, weighted discrete pick) is
factored into a shared GeneSampling used by both Generate paths.
Covered by GenomeTemplateTests (per-species centres, registry-driven
breeding, mutation override on/off).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
