- Add storage.ts utility (saveImage, deleteImageFile) for local disk operations
- Add POST /api/admin/products/[id]/images: validates MIME type and 5MB limit, saves file, creates MediaAsset record
- Add DELETE /api/admin/products/[id]/images?imageId=: removes file and DB record
- Add Images section to product edit form (hidden for new products until saved)
- Display images in square aspect-ratio grid matching storefront display
- Support multi-file upload; hover to reveal delete button
