Genetics: GenomeTemplate (per-organism gene allotment) + breed override

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>

src/MrGameEng.Content/Genetics/Genome.cs

@@ -77,12 +77,16 @@ public sealed class Genome
     /// carries, it is inherited (from that parent, on both sides) with 50% probability. Every
     /// inherited allele may then mutate per its <see cref="GeneDef"/>. <paramref name="registry"/>
     /// supplies the def for each gene id; genes absent from it are skipped.
+    /// <paramref name="mutationChance"/>, when given, overrides every gene's
+    /// <see cref="GeneDef.MutationChance"/> — letting the caller drive mutation from an evolvable
+    /// trait rather than a fixed per-gene constant.
     /// </summary>
     public static Genome Breed(
         Genome a,
         Genome b,
         IReadOnlyDictionary<string, GeneDef> registry,
-        Random random
+        Random random,
+        float? mutationChance = null
     )
     {
         var child = new Genome();
@@ -93,21 +97,22 @@ public sealed class Genome
                 continue;
             }
 
+            var chance = mutationChance ?? gene.MutationChance;
             var inA = a.Has(geneId);
             var inB = b.Has(geneId);
             if (inA && inB)
             {
                 child._alleles[geneId] = new Allele(
-                    Meiosis(gene, a[geneId], random),
-                    Meiosis(gene, b[geneId], random)
+                    Meiosis(gene, a[geneId], chance, random),
+                    Meiosis(gene, b[geneId], chance, random)
                 );
             }
             else if (random.NextSingle() < 0.5f)
             {
                 var parent = inA ? a : b;
                 child._alleles[geneId] = new Allele(
-                    Meiosis(gene, parent[geneId], random),
-                    Meiosis(gene, parent[geneId], random)
+                    Meiosis(gene, parent[geneId], chance, random),
+                    Meiosis(gene, parent[geneId], chance, random)
                 );
             }
         }
@@ -116,17 +121,17 @@ public sealed class Genome
     }
 
     // One inherited allele: pick one of the parent slot's two alleles, then maybe mutate it.
-    private static float Meiosis(GeneDef gene, Allele parent, Random random)
+    private static float Meiosis(GeneDef gene, Allele parent, float mutationChance, Random random)
     {
         var inherited = random.NextSingle() < 0.5f ? parent.A : parent.B;
-        if (random.NextSingle() >= gene.MutationChance)
+        if (random.NextSingle() >= mutationChance)
         {
             return inherited;
         }
 
         if (gene.Kind == GeneKind.Discrete)
         {
-            return PickVariant(gene, random);
+            return GeneSampling.Variant(gene, null, random);
         }
 
         var shifted =
@@ -135,49 +140,10 @@ public sealed class Genome
         return Math.Clamp(shifted, gene.Min, gene.Max);
     }
 
-    private static float GenerateAllele(GeneDef gene, Random random)
-    {
-        if (gene.Kind == GeneKind.Discrete)
-        {
-            return PickVariant(gene, random);
-        }
-
-        var value =
-            gene.Default + (random.NextSingle() * 2f - 1f) * gene.Spread * MathF.Abs(gene.Default);
-        return Math.Clamp(value, gene.Min, gene.Max);
-    }
-
-    private static float PickVariant(GeneDef gene, Random random)
-    {
-        var variants = Math.Max(1, gene.Variants);
-        if (gene.VariantWeights.Length != variants)
-        {
-            return random.Next(variants);
-        }
-
-        var total = 0f;
-        foreach (var w in gene.VariantWeights)
-        {
-            total += MathF.Max(0f, w);
-        }
-
-        if (total <= 0f)
-        {
-            return random.Next(variants);
-        }
-
-        var roll = random.NextSingle() * total;
-        for (var i = 0; i < variants; i++)
-        {
-            roll -= MathF.Max(0f, gene.VariantWeights[i]);
-            if (roll < 0f)
-            {
-                return i;
-            }
-        }
-
-        return variants - 1;
-    }
+    private static float GenerateAllele(GeneDef gene, Random random) =>
+        gene.Kind == GeneKind.Discrete
+            ? GeneSampling.Variant(gene, null, random)
+            : GeneSampling.Numeric(gene, gene.Default, gene.Spread, random);
 
     // Deterministic union of both parents' gene ids (ordered) so breeding is reproducible.
     private static IEnumerable<string> UnionKeys(Genome a, Genome b)