fix(api): key starting-sword seed idempotency on its real unique index

The CharacterItem idempotency check was looking up by the seed's own
literal id instead of the (characterId, itemDefinitionId) unique index
that CharacterItem actually enforces. If the demo character had already
looted a worn-short-sword naturally, re-running the seed would miss
that row and try to insert a colliding duplicate, breaking seeding
instead of being a safe no-op. Look up by the real domain key and reuse
whatever id is found when wiring up the CharacterEquipment row.

apps/api/src/database/seeds/vertical-slice.seed.spec.ts

@@ -419,4 +419,49 @@ describe('seedVisibleVerticalSlice', () => {
     );
     expect(characterItemRepository.rows).toHaveLength(1);
   });
+
+  it('reuses a naturally-looted starting sword instead of inserting a duplicate CharacterItem', async () => {
+    const locationRepository = new InMemoryRepository();
+    const connectionRepository = new InMemoryRepository();
+    const characterRepository = new InMemoryRepository();
+    const monsterRepository = new InMemoryRepository();
+    const locationMonsterRepository = new InMemoryRepository();
+    const characterItemRepository = new InMemoryRepository();
+    const characterEquipmentRepository = new InMemoryRepository();
+    const dataSource = createDataSource(
+      locationRepository,
+      connectionRepository,
+      characterRepository,
+      monsterRepository,
+      locationMonsterRepository,
+      new InMemoryRepository(),
+      new InMemoryRepository(),
+      new InMemoryRepository(),
+      characterItemRepository,
+      characterEquipmentRepository,
+    );
+
+    // Simulate the demo character having already looted a worn-short-sword
+    // naturally, under a DB-generated id that differs from the seed's
+    // stable literal constant.
+    const naturallyLootedItemId = 'naturally-looted-sword-item-id';
+    characterItemRepository.rows.push({
+      id: naturallyLootedItemId,
+      characterId: DEMO_CHARACTER_ID,
+      itemDefinitionId: ITEM_IDS['worn-short-sword'],
+      quantity: 1,
+    });
+
+    await seedVisibleVerticalSlice(dataSource);
+
+    expect(characterItemRepository.rows).toHaveLength(1);
+    expect(characterEquipmentRepository.rows).toHaveLength(1);
+    expect(characterEquipmentRepository.rows[0]).toEqual(
+      expect.objectContaining({
+        characterId: DEMO_CHARACTER_ID,
+        slot: 'WEAPON',
+        characterItemId: naturallyLootedItemId,
+      }),
+    );
+  });
 });