feat: cosmétiques V1 — 5 slots SVG, récompenses achievements + prestige

10 cosmétiques (2/slot), unlock auto sur achievements et prestige tiers.
TadpoleSprite composant SVG stack (base + overlays équipés).
CosmeticsPanel dans la sidebar — inventaire, équiper/retirer par slot.
GameState étendu (cosmeticInventory + cosmeticEquipped), backfill saves.
17 nouveaux tests cosmétiques (92 total, tous passent).

Frontend/src/core/cosmetics.ts

@@ -0,0 +1,97 @@
+// cosmetics.ts — Système cosmétique (récompenses achievements + prestige)
+
+import type { GameState } from "./economy";
+import { ACHIEVEMENTS } from "../data/achievements";
+
+export type CosmeticSlot = "hat" | "eyes" | "body" | "tail" | "accessory";
+
+export interface Cosmetic {
+  id: string;
+  name: string;
+  slot: CosmeticSlot;
+  svg: string;            // chemin vers le SVG overlay (/svg/cosmetics/...)
+  source: "achievement" | "prestige";
+  sourceId: string;       // achievement id ou "prestige_N"
+  description: string;
+}
+
+export interface CosmeticState {
+  inventory: string[];                          // ids des cosmétiques débloqués
+  equipped: Partial<Record<CosmeticSlot, string>>;  // slot → cosmetic id
+}
+
+export const DEFAULT_COSMETIC_STATE: CosmeticState = {
+  inventory: [],
+  equipped: {},
+};
+
+// --- Catalogue des cosmétiques ---
+
+export const COSMETICS: Cosmetic[] = [
+  // Hat
+  { id: "crown",           name: "Couronne Ancestrale",  slot: "hat",       svg: "/svg/cosmetics/crown.svg",           source: "prestige",    sourceId: "prestige_10",   description: "10 prestiges — la royauté du marais" },
+  { id: "cap_swamp",       name: "Casquette du Marais",  slot: "hat",       svg: "/svg/cosmetics/cap-swamp.svg",       source: "achievement", sourceId: "industriel",     description: "10 générateurs au total" },
+
+  // Eyes
+  { id: "glasses_savant",  name: "Lunettes du Savant",   slot: "eyes",      svg: "/svg/cosmetics/glasses-savant.svg",  source: "prestige",    sourceId: "prestige_5",    description: "5 prestiges — la sagesse" },
+  { id: "mask_frog",       name: "Masque Grenouille",    slot: "eyes",      svg: "/svg/cosmetics/mask-frog.svg",       source: "achievement", sourceId: "empire",        description: "1M têtards — le regard de l'empire" },
+
+  // Body
+  { id: "cape_algae",      name: "Cape d'Algues",        slot: "body",      svg: "/svg/cosmetics/cape-algae.svg",      source: "prestige",    sourceId: "prestige_25",   description: "25 prestiges — tissée par le marais" },
+  { id: "armor_scales",    name: "Armure d'Écailles",    slot: "body",      svg: "/svg/cosmetics/armor-scales.svg",    source: "achievement", sourceId: "tycoon",        description: "100 générateurs — blindage total" },
+
+  // Tail
+  { id: "flame_tail",      name: "Queue Enflammée",      slot: "tail",      svg: "/svg/cosmetics/flame-tail.svg",      source: "prestige",    sourceId: "prestige_50",   description: "50 prestiges — la traîne de feu" },
+  { id: "ribbon",          name: "Ruban du Nouveau-Né",  slot: "tail",      svg: "/svg/cosmetics/ribbon.svg",          source: "achievement", sourceId: "first_prestige", description: "Premier prestige — le début de tout" },
+
+  // Accessory
+  { id: "aura_swamp",      name: "Aura du Marais",       slot: "accessory", svg: "/svg/aura-swamp.svg",                source: "achievement", sourceId: "veteran",       description: "5 prestiges — l'aura des anciens" },
+  { id: "particles_gold",  name: "Particules Dorées",    slot: "accessory", svg: "/svg/cosmetics/particles-gold.svg",  source: "prestige",    sourceId: "prestige_3",    description: "3 prestiges — poussière d'étoiles" },
+];
+
+// --- Fonctions cosmétiques ---
+
+// Vérifie si un cosmétique devrait être débloqué
+export function shouldUnlockCosmetic(cosmetic: Cosmetic, state: GameState): boolean {
+  if (cosmetic.source === "prestige") {
+    const tier = parseInt(cosmetic.sourceId.replace("prestige_", ""), 10);
+    return state.prestigeCount >= tier;
+  }
+  if (cosmetic.source === "achievement") {
+    const achievement = ACHIEVEMENTS.find((a) => a.id === cosmetic.sourceId);
+    return achievement ? achievement.check(state) : false;
+  }
+  return false;
+}
+
+// Calcule les cosmétiques nouvellement débloqués (pas encore dans l'inventaire)
+export function computeNewUnlocks(state: GameState, cosmeticState: CosmeticState): string[] {
+  return COSMETICS
+    .filter((c) => !cosmeticState.inventory.includes(c.id) && shouldUnlockCosmetic(c, state))
+    .map((c) => c.id);
+}
+
+// Équiper un cosmétique (retourne le nouvel état)
+export function equipCosmetic(cosmeticState: CosmeticState, cosmeticId: string): CosmeticState {
+  const cosmetic = COSMETICS.find((c) => c.id === cosmeticId);
+  if (!cosmetic) return cosmeticState;
+  if (!cosmeticState.inventory.includes(cosmeticId)) return cosmeticState;
+
+  return {
+    ...cosmeticState,
+    equipped: { ...cosmeticState.equipped, [cosmetic.slot]: cosmeticId },
+  };
+}
+
+// Déséquiper un slot
+export function unequipSlot(cosmeticState: CosmeticState, slot: CosmeticSlot): CosmeticState {
+  const { [slot]: _, ...rest } = cosmeticState.equipped;
+  return { ...cosmeticState, equipped: rest };
+}
+
+// Ajouter des cosmétiques à l'inventaire
+export function addToInventory(cosmeticState: CosmeticState, ids: string[]): CosmeticState {
+  const newIds = ids.filter((id) => !cosmeticState.inventory.includes(id));
+  if (newIds.length === 0) return cosmeticState;
+  return { ...cosmeticState, inventory: [...cosmeticState.inventory, ...newIds] };
+}