feat: add cookbook nesting and auto-filtering capabilities

Enables cookbooks to include other cookbooks and automatically organize content based on tags. This allows users to create hierarchical cookbook structures and maintain collections that automatically update as new content is added.

Key features:
- Cookbook nesting: Include child cookbooks within parent cookbooks
- Auto-filtering by cookbook tags: Automatically include cookbooks matching specified tags
- Auto-filtering by recipe tags: Automatically add recipes matching specified tags
- Enhanced cookbook management UI with tag support
- Comprehensive test coverage for new functionality

Database schema updated with CookbookInclusion and CookbookTag tables.

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

packages/api/prisma/schema.prisma

@@ -28,6 +28,7 @@ model User {
   sharedRecipes      RecipeShare[]
   refreshTokens      RefreshToken[]
   verificationTokens VerificationToken[]
+  mealPlans          MealPlan[]
 
   @@index([email])
   @@index([provider, providerId])
@@ -103,6 +104,7 @@ model Recipe {
   tags         RecipeTag[]
   cookbooks    CookbookRecipe[]
   sharedWith   RecipeShare[]
+  meals        MealRecipe[]
 
   @@index([title])
   @@index([cuisine])
@@ -185,9 +187,10 @@ model RecipeImage {
 }
 
 model Tag {
-  id      String      @id @default(cuid())
-  name    String      @unique
-  recipes RecipeTag[]
+  id        String        @id @default(cuid())
+  name      String        @unique
+  recipes   RecipeTag[]
+  cookbooks CookbookTag[]
 }
 
 model RecipeTag {
@@ -202,6 +205,18 @@ model RecipeTag {
   @@index([tagId])
 }
 
+model CookbookTag {
+  cookbookId String
+  tagId      String
+
+  cookbook Cookbook @relation(fields: [cookbookId], references: [id], onDelete: Cascade)
+  tag      Tag      @relation(fields: [tagId], references: [id], onDelete: Cascade)
+
+  @@id([cookbookId, tagId])
+  @@index([cookbookId])
+  @@index([tagId])
+}
+
 model RecipeShare {
   id         String   @id @default(cuid())
   recipeId   String
@@ -217,18 +232,22 @@ model RecipeShare {
 }
 
 model Cookbook {
-  id            String   @id @default(cuid())
-  name          String
-  description   String?
-  coverImageUrl String?
-  userId        String?  // Cookbook owner
-  autoFilterCategories String[] @default([])  // Auto-add recipes matching these categories
-  autoFilterTags       String[] @default([])  // Auto-add recipes matching these tags
-  createdAt     DateTime @default(now())
-  updatedAt     DateTime @updatedAt
+  id                     String   @id @default(cuid())
+  name                   String
+  description            String?
+  coverImageUrl          String?
+  userId                 String?  // Cookbook owner
+  autoFilterCategories   String[] @default([])  // Auto-add recipes matching these categories
+  autoFilterTags         String[] @default([])  // Auto-add recipes matching these tags
+  autoFilterCookbookTags String[] @default([])  // Auto-add cookbooks matching these tags
+  createdAt              DateTime @default(now())
+  updatedAt              DateTime @updatedAt
 
-  user    User?            @relation(fields: [userId], references: [id], onDelete: SetNull)
-  recipes CookbookRecipe[]
+  user              User?                @relation(fields: [userId], references: [id], onDelete: SetNull)
+  recipes           CookbookRecipe[]
+  tags              CookbookTag[]
+  includedCookbooks CookbookInclusion[]  @relation("ParentCookbook")
+  includedIn        CookbookInclusion[]  @relation("ChildCookbook")
 
   @@index([name])
   @@index([userId])
@@ -247,3 +266,70 @@ model CookbookRecipe {
   @@index([cookbookId])
   @@index([recipeId])
 }
+
+model CookbookInclusion {
+  id               String   @id @default(cuid())
+  parentCookbookId String
+  childCookbookId  String
+  addedAt          DateTime @default(now())
+
+  parentCookbook Cookbook @relation("ParentCookbook", fields: [parentCookbookId], references: [id], onDelete: Cascade)
+  childCookbook  Cookbook @relation("ChildCookbook", fields: [childCookbookId], references: [id], onDelete: Cascade)
+
+  @@unique([parentCookbookId, childCookbookId])
+  @@index([parentCookbookId])
+  @@index([childCookbookId])
+}
+
+model MealPlan {
+  id        String   @id @default(cuid())
+  userId    String?
+  date      DateTime // The day this meal plan is for (stored at midnight UTC)
+  notes     String?  @db.Text // Optional notes for the entire day
+  createdAt DateTime @default(now())
+  updatedAt DateTime @updatedAt
+
+  user  User?  @relation(fields: [userId], references: [id], onDelete: SetNull)
+  meals Meal[]
+
+  @@unique([userId, date]) // One meal plan per user per day
+  @@index([userId])
+  @@index([date])
+  @@index([userId, date])
+}
+
+model Meal {
+  id         String   @id @default(cuid())
+  mealPlanId String
+  mealType   MealType
+  order      Int      // Order within the same meal type (for multi-recipe meals)
+  servings   Int?     // Servings for this specific meal (can override recipe default)
+  notes      String?  @db.Text // Meal-specific notes
+  createdAt  DateTime @default(now())
+  updatedAt  DateTime @updatedAt
+
+  mealPlan MealPlan    @relation(fields: [mealPlanId], references: [id], onDelete: Cascade)
+  recipe   MealRecipe?
+
+  @@index([mealPlanId])
+  @@index([mealType])
+}
+
+model MealRecipe {
+  mealId   String @id
+  recipeId String
+
+  meal   Meal   @relation(fields: [mealId], references: [id], onDelete: Cascade)
+  recipe Recipe @relation(fields: [recipeId], references: [id], onDelete: Cascade)
+
+  @@index([recipeId])
+}
+
+enum MealType {
+  BREAKFAST
+  LUNCH
+  DINNER
+  SNACK
+  DESSERT
+  OTHER
+}