seperate delivery and billig adresses in contract added

backend/node_modules/.prisma/client/schema.prisma

@@ -148,19 +148,20 @@ enum AddressType {
 }
 
 model Address {
-  id          Int         @id @default(autoincrement())
-  customerId  Int
-  customer    Customer    @relation(fields: [customerId], references: [id], onDelete: Cascade)
-  type        AddressType @default(DELIVERY_RESIDENCE)
-  street      String
-  houseNumber String
-  postalCode  String
-  city        String
-  country     String      @default("Deutschland")
-  isDefault   Boolean     @default(false)
-  contracts   Contract[]
-  createdAt   DateTime    @default(now())
-  updatedAt   DateTime    @updatedAt
+  id                  Int         @id @default(autoincrement())
+  customerId          Int
+  customer            Customer    @relation(fields: [customerId], references: [id], onDelete: Cascade)
+  type                AddressType @default(DELIVERY_RESIDENCE)
+  street              String
+  houseNumber         String
+  postalCode          String
+  city                String
+  country             String      @default("Deutschland")
+  isDefault           Boolean     @default(false)
+  contractsAsDelivery Contract[]  @relation("DeliveryAddress")
+  contractsAsBilling  Contract[]  @relation("BillingAddress")
+  createdAt           DateTime    @default(now())
+  updatedAt           DateTime    @updatedAt
 }
 
 // ==================== BANK CARDS ====================
@@ -481,8 +482,13 @@ model Contract {
   contractCategoryId Int?
   contractCategory   ContractCategory? @relation(fields: [contractCategoryId], references: [id])
 
+  // Lieferadresse
   addressId Int?
-  address   Address? @relation(fields: [addressId], references: [id])
+  address   Address? @relation("DeliveryAddress", fields: [addressId], references: [id])
+
+  // Rechnungsadresse (falls leer, wird Lieferadresse verwendet)
+  billingAddressId Int?
+  billingAddress   Address? @relation("BillingAddress", fields: [billingAddressId], references: [id])
 
   bankCardId Int?
   bankCard   BankCard? @relation(fields: [bankCardId], references: [id])