feat(auth): implement user authentication with JWT and NextAuth

- Added user registration and login functionality with JWT authentication.
- Created auth controller, service, and module in the backend.
- Implemented user model and user products management.
- Integrated NextAuth for session management on the frontend.
- Added middleware for protecting routes and handling public access.
- Updated frontend API routes to include authorization headers.
- Enhanced recipe and user product models to support ownership and visibility.
- Created registration and login pages in the frontend.
- Added necessary types for NextAuth session management.

backend/prisma/schema.prisma

@@ -7,6 +7,19 @@ datasource db {
   url      = env("DATABASE_URL")
 }
 
+model User {
+  id           Int          @id @default(autoincrement())
+  username     String       @unique
+  email        String       @unique
+  passwordHash String
+  createdAt    DateTime     @default(now())
+  updatedAt    DateTime     @updatedAt
+
+  userProducts UserProduct[]
+  ownedRecipes Recipe[]      @relation("RecipeOwner")
+  sharedRecipes RecipeShare[]
+}
+
 model Product {
   id             Int             @id @default(autoincrement())
   name           String
@@ -26,6 +39,28 @@ model Product {
   receiptAliases    ReceiptAlias[]
   tags              ProductTag[]
   nutrition         Nutrition?
+  ownerId           Int?
+  owner             User?           @relation(fields: [ownerId], references: [id], onDelete: SetNull)
+  userProducts      UserProduct[]
+}
+
+model UserProduct {
+  id             Int      @id @default(autoincrement())
+  userId         Int
+  productId      Int
+  note           String?  @db.Text
+  preferredBrand String?
+  preferredStore String?
+  isPrivate      Boolean  @default(false)
+  createdAt      DateTime @default(now())
+  updatedAt      DateTime @updatedAt
+
+  user    User    @relation(fields: [userId], references: [id], onDelete: Cascade)
+  product Product @relation(fields: [productId], references: [id], onDelete: Cascade)
+
+  @@unique([userId, productId])
+  @@index([userId])
+  @@index([productId])
 }
 
 model InventoryItem {
@@ -73,11 +108,25 @@ model Recipe {
   instructions String?            @db.Text
   imageUrl     String?
   servings     Int?
+  isPublic     Boolean            @default(false)
+  ownerId      Int?
   createdAt    DateTime           @default(now())
   updatedAt    DateTime           @updatedAt
 
-  ingredients   RecipeIngredient[]
+  owner           User?            @relation("RecipeOwner", fields: [ownerId], references: [id], onDelete: SetNull)
+  ingredients     RecipeIngredient[]
   mealPlanEntries MealPlanEntry[]
+  shares          RecipeShare[]
+}
+
+model RecipeShare {
+  recipeId Int
+  userId   Int
+  recipe   Recipe @relation(fields: [recipeId], references: [id], onDelete: Cascade)
+  user     User   @relation(fields: [userId], references: [id], onDelete: Cascade)
+
+  @@id([recipeId, userId])
+  @@index([userId])
 }
 
 model RecipeIngredient {