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/combat/combat.service.spec.ts

@@ -173,6 +173,7 @@ function character(overrides: Partial<Character> = {}): Character {
     name: 'Aric Duskwalker',
     level: 1,
     experience: 0,
+    silver: 0,
     baseHp: 100,
     baseAttack: 6,
     currentHp: 100,