feat: prestige threshold scales quadratically with prestige count

threshold = 1M × (1 + 0.1 × prestigeCount)² × (1 - treeReduction)

P0=1M, P5=2.25M, P10=4M, P20=9M, P50=36M
Tree reduction still applies on top. Forces strategic prestige timing
and gives the idle loop longevity.

Frontend/src/lib/core/economy.ts

@@ -683,7 +683,8 @@ export function buyGenerator(state: GameState, genId: string): GameState | null
 
 export function getPrestigeThreshold(state: GameState): number {
   const reduction = getPrestigeThresholdReduction(state.evolutionTree);
-  return Math.floor(BASE_PRESTIGE_THRESHOLD * (1 - reduction));
+  const scaling = Math.pow(1 + 0.1 * state.prestigeCount, 2);
+  return Math.floor(BASE_PRESTIGE_THRESHOLD * scaling * (1 - reduction));
 }
 
 export function canPrestige(state: GameState): boolean {