feat: arbre d'évolution 3 voies — ponte/marais/adaptation

18 nœuds (6/branche), nœuds exclusifs (pick one), reset gratuit.
Nouveaux effets : double_click, auto_click, crit, generator_boost,
cost_reduction, prestige_dna_bonus, offline_boost, threshold_reduction.
UI 3 colonnes colorées, seuil prestige dynamique, coût réduit.
75 tests (tous passent).

Frontend/src/components/GeneratorShop.tsx

@@ -8,7 +8,7 @@ export function GeneratorShop() {
   const resources = useGameStore((s) => s.state.resources);
   const productionPerSecond = useGameStore((s) => s.productionPerSecond);
   const buy = useGameStore((s) => s.buy);
-  const generatorCost = useGameStore((s) => s.generatorCost);
+  const generatorCost = useGameStore((s) => s.generatorCostWithTree);
 
   return (
     <div className="gp">