Fix Pet entity ID mapping for JPA compatibility

src/main/java/com/petshop/backend/entity/Pet.java

@@ -14,7 +14,8 @@ public class Pet {
 
     @Id
     @GeneratedValue(strategy = GenerationType.IDENTITY)
-    private Long petId;
+    @Column(name = "petId")
+    private Long id;
 
     @Column(nullable = false, length = 50)
     private String petName;
@@ -45,8 +46,8 @@ public class Pet {
     public Pet() {
     }
 
-    public Pet(Long petId, String petName, String petSpecies, String petBreed, Integer petAge, String petStatus, BigDecimal petPrice, LocalDateTime createdAt, LocalDateTime updatedAt) {
-        this.petId = petId;
+    public Pet(Long id, String petName, String petSpecies, String petBreed, Integer petAge, String petStatus, BigDecimal petPrice, LocalDateTime createdAt, LocalDateTime updatedAt) {
+        this.id = id;
         this.petName = petName;
         this.petSpecies = petSpecies;
         this.petBreed = petBreed;
@@ -58,11 +59,11 @@ public class Pet {
     }
 
     public Long getPetId() {
-        return petId;
+        return id;
     }
 
-    public void setPetId(Long petId) {
-        this.petId = petId;
+    public void setPetId(Long id) {
+        this.id = id;
     }
 
     public String getPetName() {
@@ -134,18 +135,18 @@ public class Pet {
         if (this == o) return true;
         if (o == null || getClass() != o.getClass()) return false;
         Pet pet = (Pet) o;
-        return Objects.equals(petId, pet.petId);
+        return Objects.equals(id, pet.id);
     }
 
     @Override
     public int hashCode() {
-        return Objects.hash(petId);
+        return Objects.hash(id);
     }
 
     @Override
     public String toString() {
         return "Pet{" +
-                "petId=" + petId +
+                "id=" + id +
                 ", petName='" + petName + '\'' +
                 ", petSpecies='" + petSpecies + '\'' +
                 ", petBreed='" + petBreed + '\'' +