Add isUsed on store items with API list filters.

Persists used/second-hand status per listing and supports isUsed=true on business and public store-item queries.

Co-authored-by: Cursor <cursoragent@cursor.com>

prisma/schema.prisma

@@ -1141,6 +1141,7 @@ model StoreItem {
   businessId   BigInt             @map("business_id")
   productId    BigInt             @map("product_id")
   isActive     Boolean            @default(true) @map("is_active")
+  isUsed       Boolean            @default(false) @map("is_used")
   sortOrder    Int                @default(0) @map("sort_order")
   createdAt    DateTime           @default(now()) @map("created_at") @db.Timestamptz(6)
   updatedAt    DateTime           @default(now()) @updatedAt @map("updated_at") @db.Timestamptz(6)
@@ -1152,6 +1153,7 @@ model StoreItem {
   @@unique([businessId, productId], map: "store_items_business_product_unique")
   @@index([businessId], map: "idx_store_items_business_id")
   @@index([productId], map: "idx_store_items_product_id")
+  @@index([businessId, isUsed], map: "idx_store_items_business_is_used")
   @@map("store_items")
 }