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/items/equipment-slot.enum.ts

@@ -0,0 +1,10 @@
+// Slice 0.4 only stores the slot as content data. Slice 0.5 makes it functional.
+export enum EquipmentSlot {
+  WEAPON = 'WEAPON',
+  HEAD = 'HEAD',
+  CHEST = 'CHEST',
+  HANDS = 'HANDS',
+  LEGS = 'LEGS',
+  FEET = 'FEET',
+  AMULET = 'AMULET',
+}