feat: Sprint 2 — moteur de combat PvE TetaRdPG

Moteur combat stateless (POST /api/combat/start résout le combat complet).
Formules GDD : Mêlée/Distance/Magie × 1.5, critique (5% + Chance×0.2%), esquive (5% + Chance×0.1%).
5 monstres seedés (Têtard Vase → Golem de Boue, level 1–9).
Level up : XP → seuil atteint → level++, +5 statPoints.
Persiste combat_logs (jsonb rounds). Validé : victoire, défaite, 401, 400, 404.

src/monster/monster.entity.ts

@@ -0,0 +1,39 @@
+import { Entity, PrimaryGeneratedColumn, Column } from 'typeorm';
+
+export type AttackType = 'melee' | 'ranged' | 'magic';
+
+@Entity('monsters')
+export class Monster {
+  @PrimaryGeneratedColumn('uuid')
+  id: string;
+
+  @Column({ length: 100 })
+  name: string;
+
+  @Column({ name: 'min_level' })
+  minLevel: number;
+
+  @Column({ name: 'max_level' })
+  maxLevel: number;
+
+  @Column()
+  hp: number;
+
+  @Column()
+  attack: number;
+
+  @Column({ default: 0 })
+  defense: number;
+
+  @Column({ name: 'attack_type', type: 'varchar', length: 20 })
+  attackType: AttackType;
+
+  @Column({ name: 'xp_reward' })
+  xpReward: number;
+
+  @Column({ name: 'gold_min' })
+  goldMin: number;
+
+  @Column({ name: 'gold_max' })
+  goldMax: number;
+}