fix: particule clic affiche le vrai gain (clickMult × prestigeMult × treeMult)

Ajout getClickGain() dans economy.ts — utilisé par la particule de feedback
et le cockpit header "Ponte". Avant : affichait toujours +1.

Frontend/src/core/economy.ts

@@ -129,10 +129,15 @@ export function applyIdleGains(state: GameState, now: number): GameState {
   };
 }
 
+// Gain réel par clic (pour affichage particule)
+export function getClickGain(state: GameState): number {
+  const treeClickMult = getClickMultiplierFromTree(state.evolutionTree);
+  return state.clickMultiplier * state.prestigeMultiplier * treeClickMult;
+}
+
 // Clic manuel
 export function applyClick(state: GameState): GameState {
-  const treeClickMult = getClickMultiplierFromTree(state.evolutionTree);
-  const gain = state.clickMultiplier * state.prestigeMultiplier * treeClickMult;
+  const gain = getClickGain(state);
   return {
     ...state,
     resources: state.resources + gain,