Birth type gene (live-bearing vs egg-laying) + hybrid-creation foundation

GeneEggLaying (species-fixed) selects the conception cycle: viviparous animals
carry to a live birth (existing path); oviparous animals, after the same gravid
period, LAY eggs instead. New Egg entity (carries the already-bred offspring
genome) + EggSystem incubates and hatches it into a baby. AnimalPregnancySystem
branches on the mother's birth type. Adds an oviparous showcase species, Chicken.
Eggs are serialized (WorldSave.Eggs) like corpses, so clutches survive save/load.

Also lays the foundation for creating any species or hybrid (full command/UI
deferred): AnimalSet.HybridGenome(base, other) produces a cross anchored to a
base species' body/gene-set with shared genes blended Mendelian-style — so
Create(species, GenerateGenome) makes any species and Create(species,
HybridGenome) makes any hybrid.

EggTexture on AnimalDef (defaults to the seed dot placeholder); reproduction line
added to the `animal` console command. Build + --check-content clean (41 genes,
40 traits). Not GUI-verified.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Mods/Core/Defs/Genes/Animal.json

@@ -59,6 +59,13 @@
     { "defName": "GeneSex", "kind": "Discrete", "label": "gene.sex",
       "variants": 2, "variantWeights": [0.5, 0.5], "mutationChance": 0, "tags": ["animal", "sex"] },
 
+    // Тип рождения (цикл зачатия): живородящие (eggLaying < 0.5) вынашивают и рожают живых детёнышей;
+    // яйцекладущие (≥ 0.5) после вынашивания ОТКЛАДЫВАЮТ яйца-сущности, которые инкубируются и
+    // вылупляются (см. AnimalPregnancySystem/EggSystem). Признак фиксирован по виду (spread/mutation 0).
+    { "defName": "GeneEggLaying", "parent": "BaseNumericGene", "label": "gene.eggLaying",
+      "default": 0.0, "min": 0.0, "max": 1.0, "spread": 0, "mutationChance": 0, "tags": ["animal", "reproduction"],
+      "effects": { "eggLaying": "value" } },
+
     // Размножение (фаза A4): сезон гона фиксирован по виду (0 весна … 3 зима), срок вынашивания и помёт.
     { "defName": "GeneBreedingSeason", "parent": "BaseNumericGene", "label": "gene.breedingSeason",
       "default": 2, "min": 0, "max": 3, "spread": 0, "mutationChance": 0, "tags": ["animal", "reproduction"],