Commit design approval workflow and related features

- Add design approval workflow components and API routes
- Update checkout process for design approval integration
- Add admin navigation for design management
- Update mail utilities for design notifications
- Update types for design approval system
- Update Prisma schema for design approval database

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

prisma/schema.prisma

@@ -39,6 +39,8 @@ model Product {
   printAreaBack String? // same shape, for the back print area — only used when imageUrlBack is set
   printAreaWidthMm Int @default(200) // width of the printable area in millimeters
   printAreaHeightMm Int @default(280) // height of the printable area in millimeters
+  referenceWidthCm Int? // width of garment/object for ruler reference (cm)
+  referenceHeightCm Int? // height of garment/object for ruler reference (cm)
   imageUrl    String? // optional real product photo — shown instead of the illustration when set
   imageUrlBack String? // optional back-view photo, toggled alongside the front photo
   photoRecolorable Boolean @default(false) // if true, the photo is treated as a grayscale
@@ -53,15 +55,16 @@ model Product {
   saleStartsAt DateTime? // leave null to start the sale immediately
   saleEndsAt   DateTime? // leave null for an open-ended sale
 
-  orderItems      OrderItem[]
-  proofs          DesignProof[]
-  customRequests  CustomRequest[]
-  promotions      Promotion[] // only relevant to promotions scoped to specific items, not "all items"
-  collections     Collection[] // occasion/recipient tags, e.g. "Christmas", "For Teachers"
-  manualSaleItems ManualSaleItem[]
-  stockLevels     StockLevel[]
-  purchaseItems   PurchaseItem[]
-  productImages   ProductImage[]
+  orderItems        OrderItem[]
+  proofs            DesignProof[]
+  customRequests    CustomRequest[]
+  designApprovals   DesignApproval[]
+  promotions        Promotion[] // only relevant to promotions scoped to specific items, not "all items"
+  collections       Collection[] // occasion/recipient tags, e.g. "Christmas", "For Teachers"
+  manualSaleItems   ManualSaleItem[]
+  stockLevels       StockLevel[]
+  purchaseItems     PurchaseItem[]
+  productImages     ProductImage[]
 }
 
 // Bulk-uploaded product images with auto-detected colors. Supports any product type
@@ -174,6 +177,41 @@ model Message {
   createdAt DateTime    @default(now())
 }
 
+// Customer-submitted designs pending admin approval before checkout
+model DesignApproval {
+  id                   String   @id @default(cuid())
+  customerId           String?  // null for guest customers
+  customer             Customer? @relation(fields: [customerId], references: [id], onDelete: SetNull)
+  customerEmail        String
+  customerName         String?
+  productId            String
+  product              Product  @relation(fields: [productId], references: [id])
+  designJson           String   // serialized {front:[...], back:[...]} design elements
+  designPreviewUrl     String   // base64 PNG data URL — front design, transparent, print-ready
+  designPreviewUrlBack String?  // same, for the back design if there is one
+  placementPreviewUrl  String?  // front design on product photo
+  placementPreviewUrlBack String? // back design on product photo
+  designWidthCm        Float?   // width of design in centimeters (legacy, for backward compatibility)
+  designHeightCm       Float?   // height of design in centimeters (legacy, for backward compatibility)
+  designImageDimensions String?  // JSON array of {imageId, widthCm, heightCm} for each uploaded image
+  color                String
+  size                 String?
+  status               String   @default("PENDING") // PENDING | APPROVED | REJECTED
+  messages             DesignApprovalMessage[]
+  createdAt            DateTime @default(now())
+  updatedAt            DateTime @updatedAt
+}
+
+// Chat messages for design approval discussions
+model DesignApprovalMessage {
+  id           String         @id @default(cuid())
+  designId     String
+  design       DesignApproval @relation(fields: [designId], references: [id], onDelete: Cascade)
+  sender       String         // "ADMIN" | "CUSTOMER"
+  body         String
+  createdAt    DateTime       @default(now())
+}
+
 model Order {
   id              String      @id @default(cuid())
   stripeSessionId String?     @unique
@@ -207,6 +245,7 @@ model Customer {
   passwordResetToken PasswordResetToken?
   customRequests     CustomRequest[]
   manualSales        ManualSale[]
+  designApprovals    DesignApproval[]
 }
 
 // A sale that didn't go through the website checkout — cash at a fair, a bank
@@ -383,6 +422,9 @@ model OrderItem {
   designPreviewUrlBack String? // same, for the back design if there is one
   placementPreviewUrl     String? // front design shown composited on the actual product photo, for reference — where does this go when printing
   placementPreviewUrlBack String? // same, for the back
+  designWidthCm        Float? // width of design in centimeters (legacy)
+  designHeightCm       Float? // height of design in centimeters (legacy)
+  designImageDimensions String? // JSON array of {imageId, widthCm, heightCm} for each uploaded image
 }
 
 // Audit log for admin logins — tracks when the admin panel is accessed