feat(loot): add item, loot table, and combat reward entities

Declares every new TypeORM entity Slice 0.4 needs (ItemDefinition,
CharacterItem, LootTable, LootTableEntry, CombatReward, CombatRewardItem)
plus the ItemType/EquipmentSlot/ItemRarity enums, and adds the two columns
existing entities gain: Character.silver and MonsterDefinition.lootTableId.
No migration SQL or service logic yet - just schema declarations backed by
a metadata-driven schema spec.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

apps/api/src/characters/entities/character.entity.ts

@@ -23,6 +23,9 @@ export class Character {
   @Column({ name: 'experience', type: 'integer' })
   experience!: number;
 
+  @Column({ name: 'silver', type: 'integer' })
+  silver!: number;
+
   @Column({ name: 'base_hp', type: 'integer' })
   baseHp!: number;