feat: PantryItem (Baslager) - tabell, backend-modul och frontend-sida

backend/prisma/schema.prisma

@@ -18,8 +18,9 @@ model Product {
   createdAt      DateTime        @default(now())
   updatedAt      DateTime        @updatedAt
 
-  inventoryItems InventoryItem[]
+  inventoryItems    InventoryItem[]
   recipeIngredients RecipeIngredient[]
+  pantryItems       PantryItem[]
 }
 
 model InventoryItem {
@@ -81,6 +82,14 @@ model RecipeIngredient {
   unit      String
   note      String?
 
+  createdAt DateTime @default(now())
+  updatedAt DateTime @updatedAt
+}
+
+model PantryItem {
+  id        Int      @id @default(autoincrement())
+  productId Int      @unique
+  product   Product  @relation(fields: [productId], references: [id], onDelete: Cascade)
   createdAt DateTime @default(now())
   updatedAt DateTime @updatedAt
 }