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/entities/character-item.entity.ts

@@ -0,0 +1,51 @@
+import {
+  Column,
+  CreateDateColumn,
+  Entity,
+  Index,
+  JoinColumn,
+  ManyToOne,
+  PrimaryGeneratedColumn,
+  UpdateDateColumn,
+} from 'typeorm';
+import { Character } from '../../characters/entities/character.entity';
+import { ItemDefinition } from './item-definition.entity';
+
+/**
+ * One stack of one item definition owned by one character.
+ *
+ * Duplicate drops increment `quantity` (spec §28 allows duplicates and forbids
+ * duplicate protection). Slice 0.5 equips a `CharacterItem.id`, never an
+ * `ItemDefinition.id`.
+ */
+@Entity({ name: 'character_items' })
+@Index('IDX_character_items_character_item', ['characterId', 'itemDefinitionId'], {
+  unique: true,
+})
+export class CharacterItem {
+  @PrimaryGeneratedColumn('uuid', { name: 'id' })
+  id!: string;
+
+  @Column({ name: 'character_id', type: 'uuid' })
+  characterId!: string;
+
+  @Column({ name: 'item_definition_id', type: 'uuid' })
+  itemDefinitionId!: string;
+
+  @Column({ name: 'quantity', type: 'integer' })
+  quantity!: number;
+
+  @CreateDateColumn({ name: 'created_at', type: 'timestamptz' })
+  createdAt!: Date;
+
+  @UpdateDateColumn({ name: 'updated_at', type: 'timestamptz' })
+  updatedAt!: Date;
+
+  @ManyToOne(() => Character, { onDelete: 'CASCADE' })
+  @JoinColumn({ name: 'character_id' })
+  character!: Character;
+
+  @ManyToOne(() => ItemDefinition, { onDelete: 'RESTRICT' })
+  @JoinColumn({ name: 'item_definition_id' })
+  itemDefinition!: ItemDefinition;
+}