feat(sprint5): quest system + arcs + rebalance endurance/damage/xp

Quest system:
  4 entities (quest_arcs, quests, player_quests, player_quest_arcs)
  Arc "Les Marais du Têtard" (4 quêtes narratives)
  3 quêtes standalone répétables (chasse/forge/craft)
  5 achievements liés (quests_completed + quest_arc_completed)
  Event-driven: combat/forge/craft/loot émettent quest.progress
  API: available, active, completed, accept, claim, arcs

Rebalance:
  Endurance coût combat 10→5, regen 6min→3min (20/h), repos 20→10
  Dégâts joueur +3 base (plus de combats de 13 tours au level 1)
  Défaite endurance penalty 50→25
  XP monstres réduite (25→8 Têtard, 130→50 Golem) — quêtes = source principale

src/quest/quest-arc.entity.ts

@@ -0,0 +1,31 @@
+import {
+  Entity,
+  PrimaryGeneratedColumn,
+  Column,
+  OneToMany,
+} from 'typeorm';
+import { Quest } from './quest.entity';
+
+@Entity('quest_arcs')
+export class QuestArc {
+  @PrimaryGeneratedColumn('uuid')
+  id: string;
+
+  @Column({ length: 100 })
+  name: string;
+
+  @Column('text')
+  description: string;
+
+  @Column({ length: 50, nullable: true, type: 'varchar' })
+  zone: string | null; // 'marais', 'foret', etc.
+
+  @Column({ name: 'sort_order', default: 0 })
+  sortOrder: number;
+
+  @Column({ name: 'min_level', default: 1 })
+  minLevel: number;
+
+  @OneToMany(() => Quest, (q) => q.arc)
+  quests: Quest[];
+}