Entity 클래스 및 서비스 로직 개선

- kos-mock Entity 클래스 개선 (BillEntity, CustomerEntity, ProductEntity)
- user-service Entity 클래스 개선 (AuthUserEntity, AuthUserPermissionEntity)
- UserService 로직 개선
- kos-mock 데이터베이스 업데이트

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

kos-mock/src/main/java/com/phonebill/kosmock/entity/BillEntity.java

@@ -62,9 +62,10 @@ public class BillEntity {
     private String dueDate;
     
     @CreationTimestamp
-    @Column(name = "created_at", nullable = false)
-    private LocalDateTime createdAt;
-    
+    @Column(name = "created_at", nullable = false, updatable = false)
+    @Builder.Default
+    private LocalDateTime createdAt = LocalDateTime.now();
+
     // 고객 정보와의 관계
     @ManyToOne(fetch = FetchType.LAZY)
     @JoinColumn(name = "line_number", insertable = false, updatable = false)

kos-mock/src/main/java/com/phonebill/kosmock/entity/CustomerEntity.java

@@ -41,12 +41,14 @@ public class CustomerEntity {
     private LocalDateTime contractDate;
     
     @CreationTimestamp
-    @Column(name = "created_at", nullable = false)
-    private LocalDateTime createdAt;
-    
+    @Column(name = "created_at", nullable = false, updatable = false)
+    @Builder.Default
+    private LocalDateTime createdAt = LocalDateTime.now();
+
     @UpdateTimestamp
     @Column(name = "updated_at", nullable = false)
-    private LocalDateTime updatedAt;
+    @Builder.Default
+    private LocalDateTime updatedAt = LocalDateTime.now();
     
     // 상품 엔티티와의 관계 설정 (조회 성능을 위해)
     @ManyToOne(fetch = FetchType.LAZY)

kos-mock/src/main/java/com/phonebill/kosmock/entity/ProductEntity.java

@@ -54,10 +54,12 @@ public class ProductEntity {
     private String description;
     
     @CreationTimestamp
-    @Column(name = "created_at", nullable = false)
-    private LocalDateTime createdAt;
-    
+    @Column(name = "created_at", nullable = false, updatable = false)
+    @Builder.Default
+    private LocalDateTime createdAt = LocalDateTime.now();
+
     @UpdateTimestamp
     @Column(name = "updated_at", nullable = false)
-    private LocalDateTime updatedAt;
+    @Builder.Default
+    private LocalDateTime updatedAt = LocalDateTime.now();
 }