feat(sprint1-step2): core economy TS + useEconomy hook (lazy calc) + 13 tests vitest

Frontend/src/core/economy.ts

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+// economy.ts — Core clicker logic (lazy calculation pattern)
+// Jamais de timer actif : tout est calculé au read depuis lastTick
+
+export interface Generator {
+  id: string;
+  name: string;
+  baseCost: number;
+  baseProduction: number; // ressource/s
+  owned: number;
+}
+
+export interface GameState {
+  resources: number;
+  clickMultiplier: number;
+  generators: Generator[];
+  lastTick: number; // timestamp ms — lazy calc reference
+  prestigeCount: number;
+  prestigeMultiplier: number; // 1 + prestigeCount * 0.1
+}
+
+// Coût d'achat du N-ième générateur : baseCost × 1.15^owned
+export function generatorCost(gen: Generator): number {
+  return Math.floor(gen.baseCost * Math.pow(1.15, gen.owned));
+}
+
+// Production totale par seconde de tous les générateurs
+export function totalProductionPerSecond(state: GameState): number {
+  const base = state.generators.reduce(
+    (sum, gen) => sum + gen.baseProduction * gen.owned,
+    0
+  );
+  return base * state.prestigeMultiplier;
+}
+
+// Lazy calculation : ressources accumulées depuis lastTick
+export function computeIdleGains(state: GameState, now: number): number {
+  const elapsedSeconds = (now - state.lastTick) / 1000;
+  return totalProductionPerSecond(state) * elapsedSeconds;
+}
+
+// Applique les gains idle et met à jour lastTick
+export function applyIdleGains(state: GameState, now: number): GameState {
+  const gains = computeIdleGains(state, now);
+  return {
+    ...state,
+    resources: state.resources + gains,
+    lastTick: now,
+  };
+}
+
+// Clic manuel
+export function applyClick(state: GameState): GameState {
+  return {
+    ...state,
+    resources: state.resources + state.clickMultiplier * state.prestigeMultiplier,
+  };
+}
+
+// Achat d'un générateur (retourne null si fonds insuffisants)
+export function buyGenerator(state: GameState, genId: string): GameState | null {
+  const genIndex = state.generators.findIndex((g) => g.id === genId);
+  if (genIndex === -1) return null;
+
+  const gen = state.generators[genIndex];
+  const cost = generatorCost(gen);
+  if (state.resources < cost) return null;
+
+  const updatedGenerators = [...state.generators];
+  updatedGenerators[genIndex] = { ...gen, owned: gen.owned + 1 };
+
+  return {
+    ...state,
+    resources: state.resources - cost,
+    generators: updatedGenerators,
+  };
+}
+
+// Prestige : reset ressources + générateurs, +0.1× multiplicateur permanent
+export function canPrestige(state: GameState): boolean {
+  return state.resources >= 1_000_000;
+}
+
+export function applyPrestige(state: GameState): GameState {
+  const newPrestigeCount = state.prestigeCount + 1;
+  return {
+    ...state,
+    resources: 0,
+    generators: state.generators.map((g) => ({ ...g, owned: 0 })),
+    prestigeCount: newPrestigeCount,
+    prestigeMultiplier: 1 + newPrestigeCount * 0.1,
+    lastTick: Date.now(),
+  };
+}
+
+// Valeurs par défaut — 5 tiers alignés GDD (x10 coût / tier, x5 production)
+export const DEFAULT_GENERATORS: Generator[] = [
+  { id: "manic",   name: "Manic",        baseCost: 10,      baseProduction: 0.1,  owned: 0 },
+  { id: "coffee",  name: "Tasse à café", baseCost: 100,     baseProduction: 0.5,  owned: 0 },
+  { id: "sugar",   name: "Sucre",        baseCost: 1_000,   baseProduction: 3,    owned: 0 },
+  { id: "factory", name: "Usine",        baseCost: 10_000,  baseProduction: 20,   owned: 0 },
+  { id: "portal",  name: "Portail",      baseCost: 100_000, baseProduction: 150,  owned: 0 },
+];
+
+export const DEFAULT_STATE: GameState = {
+  resources: 0,
+  clickMultiplier: 1,
+  generators: DEFAULT_GENERATORS,
+  lastTick: Date.now(),
+  prestigeCount: 0,
+  prestigeMultiplier: 1,
+};