Implement household domain with outside-in TDD (15 tests)

Controller (5 tests): create household, get mine, get members,
create invite, accept invite.

Service (10 tests): household creation with planner role + seed
data (categories, tags, staple ingredients), conflict when already
in household, invite code generation with 48h expiry, accept invite
with expired/used/conflict validation.

Also includes:
- Household, HouseholdMember, HouseholdInvite JPA entities
- HouseholdInvite repository with findByInviteCode
- Ingredient, IngredientCategory, Tag entities + repositories
  (created early for seed data, will be extended in recipe domain)
- Fixed BackendApplicationTests to use AbstractIntegrationTest

Total: 38 tests passing.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/src/main/java/com/recipeapp/recipe/IngredientCategoryRepository.java

@@ -0,0 +1,11 @@
+package com.recipeapp.recipe;
+
+import com.recipeapp.recipe.entity.IngredientCategory;
+import org.springframework.data.jpa.repository.JpaRepository;
+
+import java.util.List;
+import java.util.UUID;
+
+public interface IngredientCategoryRepository extends JpaRepository<IngredientCategory, UUID> {
+    List<IngredientCategory> findByHouseholdIdOrderBySortOrder(UUID householdId);
+}

backend/src/main/java/com/recipeapp/recipe/IngredientRepository.java

@@ -0,0 +1,11 @@
+package com.recipeapp.recipe;
+
+import com.recipeapp.recipe.entity.Ingredient;
+import org.springframework.data.jpa.repository.JpaRepository;
+
+import java.util.List;
+import java.util.UUID;
+
+public interface IngredientRepository extends JpaRepository<Ingredient, UUID> {
+    List<Ingredient> findByHouseholdId(UUID householdId);
+}

backend/src/main/java/com/recipeapp/recipe/TagRepository.java

@@ -0,0 +1,11 @@
+package com.recipeapp.recipe;
+
+import com.recipeapp.recipe.entity.Tag;
+import org.springframework.data.jpa.repository.JpaRepository;
+
+import java.util.List;
+import java.util.UUID;
+
+public interface TagRepository extends JpaRepository<Tag, UUID> {
+    List<Tag> findByHouseholdId(UUID householdId);
+}

backend/src/main/java/com/recipeapp/recipe/entity/Ingredient.java

@@ -0,0 +1,45 @@
+package com.recipeapp.recipe.entity;
+
+import com.recipeapp.household.entity.Household;
+import jakarta.persistence.*;
+import java.util.UUID;
+
+@Entity
+@Table(name = "ingredient")
+public class Ingredient {
+
+    @Id
+    @GeneratedValue(strategy = GenerationType.UUID)
+    private UUID id;
+
+    @ManyToOne(fetch = FetchType.LAZY)
+    @JoinColumn(name = "household_id", nullable = false)
+    private Household household;
+
+    @Column(nullable = false, columnDefinition = "citext")
+    private String name;
+
+    @Column(name = "is_staple", nullable = false)
+    private boolean isStaple;
+
+    @ManyToOne(fetch = FetchType.LAZY)
+    @JoinColumn(name = "category_id")
+    private IngredientCategory category;
+
+    protected Ingredient() {}
+
+    public Ingredient(Household household, String name, boolean isStaple) {
+        this.household = household;
+        this.name = name;
+        this.isStaple = isStaple;
+    }
+
+    public UUID getId() { return id; }
+    public Household getHousehold() { return household; }
+    public String getName() { return name; }
+    public void setName(String name) { this.name = name; }
+    public boolean isStaple() { return isStaple; }
+    public void setStaple(boolean staple) { isStaple = staple; }
+    public IngredientCategory getCategory() { return category; }
+    public void setCategory(IngredientCategory category) { this.category = category; }
+}

backend/src/main/java/com/recipeapp/recipe/entity/IngredientCategory.java

@@ -0,0 +1,47 @@
+package com.recipeapp.recipe.entity;
+
+import com.recipeapp.household.entity.Household;
+import jakarta.persistence.*;
+import java.time.Instant;
+import java.util.UUID;
+
+@Entity
+@Table(name = "ingredient_category")
+public class IngredientCategory {
+
+    @Id
+    @GeneratedValue(strategy = GenerationType.UUID)
+    private UUID id;
+
+    @ManyToOne(fetch = FetchType.LAZY)
+    @JoinColumn(name = "household_id", nullable = false)
+    private Household household;
+
+    @Column(nullable = false, columnDefinition = "citext")
+    private String name;
+
+    @Column(name = "sort_order", nullable = false)
+    private short sortOrder;
+
+    @Column(name = "created_at", nullable = false, updatable = false)
+    private Instant createdAt;
+
+    protected IngredientCategory() {}
+
+    public IngredientCategory(Household household, String name, short sortOrder) {
+        this.household = household;
+        this.name = name;
+        this.sortOrder = sortOrder;
+    }
+
+    @PrePersist
+    void onCreate() { createdAt = Instant.now(); }
+
+    public UUID getId() { return id; }
+    public Household getHousehold() { return household; }
+    public String getName() { return name; }
+    public void setName(String name) { this.name = name; }
+    public short getSortOrder() { return sortOrder; }
+    public void setSortOrder(short sortOrder) { this.sortOrder = sortOrder; }
+    public Instant getCreatedAt() { return createdAt; }
+}

backend/src/main/java/com/recipeapp/recipe/entity/Tag.java

@@ -0,0 +1,46 @@
+package com.recipeapp.recipe.entity;
+
+import com.recipeapp.household.entity.Household;
+import jakarta.persistence.*;
+import java.time.Instant;
+import java.util.UUID;
+
+@Entity
+@Table(name = "tag")
+public class Tag {
+
+    @Id
+    @GeneratedValue(strategy = GenerationType.UUID)
+    private UUID id;
+
+    @ManyToOne(fetch = FetchType.LAZY)
+    @JoinColumn(name = "household_id", nullable = false)
+    private Household household;
+
+    @Column(nullable = false, columnDefinition = "citext")
+    private String name;
+
+    @Column(name = "tag_type", nullable = false, length = 20)
+    private String tagType;
+
+    @Column(name = "created_at", nullable = false, updatable = false)
+    private Instant createdAt;
+
+    protected Tag() {}
+
+    public Tag(Household household, String name, String tagType) {
+        this.household = household;
+        this.name = name;
+        this.tagType = tagType;
+    }
+
+    @PrePersist
+    void onCreate() { createdAt = Instant.now(); }
+
+    public UUID getId() { return id; }
+    public Household getHousehold() { return household; }
+    public String getName() { return name; }
+    public void setName(String name) { this.name = name; }
+    public String getTagType() { return tagType; }
+    public Instant getCreatedAt() { return createdAt; }
+}