Add ProductImage schema for bulk image upload

- ProductImage model links images to products with detected color
- Supports any product type (tees, hoodies, mugs, etc.)
- One image per color per product (unique constraint)

Bulk upload form + color detection coming next.

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

prisma/schema.prisma

@@ -60,6 +60,21 @@ model Product {
   manualSaleItems ManualSaleItem[]
   stockLevels     StockLevel[]
   purchaseItems   PurchaseItem[]
+  productImages   ProductImage[]
+}
+
+// Bulk-uploaded product images with auto-detected colors. Supports any product type
+// (tees, hoodies, mugs, etc.). User uploads a folder, colors are extracted, then saved
+// as color-swatch references for the product's color palette.
+model ProductImage {
+  id            String   @id @default(cuid())
+  productId     String
+  product       Product  @relation(fields: [productId], references: [id], onDelete: Cascade)
+  color         String // hex color detected from the image, e.g. "#1EA7E0"
+  imageDataUrl  String // the uploaded image itself as a data URL
+  createdAt     DateTime @default(now())
+
+  @@unique([productId, color])
 }
 
 // Quantity on hand for one product/colour/size combination. Purchases increase