feat: multi-combat ×5/×10 + cooldown anti-spam

- Backend: startMultiCombat boucle séquentielle, arrêt sur défaite
- Frontend: cooldown 1.5s entre combats, boutons ×1/×5/×10
- Frontend: résumé multi-combat (wins/losses, XP/Or/loot totaux)
- Fix: lock contention par spam de clics résolu

src/combat/combat.service.ts

@@ -287,6 +287,40 @@ export class CombatService {
     return txResult.response;
   }
 
+  async startMultiCombat(dto: StartCombatDto, user: User, count: number) {
+    const results: any[] = [];
+    const totals = { wins: 0, losses: 0, xp: 0, gold: 0, goldLost: 0, loot: [] as { name: string; quantity: number }[], levelsGained: 0 };
+
+    for (let i = 0; i < count; i++) {
+      try {
+        const result = await this.startCombat(dto, user);
+        results.push(result);
+        if (result.winner === 'player') {
+          totals.wins++;
+          totals.xp += result.rewards.xp;
+          totals.gold += result.rewards.gold;
+          if (result.rewards.levelUp) totals.levelsGained++;
+          if (result.rewards.loot) totals.loot.push(result.rewards.loot);
+        } else {
+          totals.losses++;
+          totals.goldLost += result.rewards.goldLost ?? 0;
+          break; // Défaite = arrêt de la série
+        }
+      } catch {
+        break; // Endurance insuffisante ou autre erreur = arrêt
+      }
+    }
+
+    const lastResult = results[results.length - 1];
+    return {
+      mode: 'multi',
+      count: results.length,
+      totals,
+      lastResult,
+      character: lastResult?.character,
+    };
+  }
+
   async getHistory(user: User) {
     const character = await this.characterRepository.findOne({
       where: { userId: user.id },