refactor: 모델에 JSON 태그 추가 및 gorm.Model 인라인 확장

camelCase JSON 필드명으로 통일, PasswordHash json:"-" 처리

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

internal/auth/model.go

@@ -1,6 +1,10 @@
 package auth
 
-import "gorm.io/gorm"
+import (
+	"time"
+
+	"gorm.io/gorm"
+)
 
 type Role string
 
@@ -10,8 +14,11 @@ const (
 )
 
 type User struct {
-	gorm.Model
-	Username     string `gorm:"type:varchar(100);uniqueIndex;not null"`
-	PasswordHash string `gorm:"not null"`
-	Role         Role   `gorm:"default:'user'"`
+	ID           uint           `json:"id"        gorm:"primaryKey"`
+	CreatedAt    time.Time      `json:"createdAt"`
+	UpdatedAt    time.Time      `json:"updatedAt"`
+	DeletedAt    gorm.DeletedAt `json:"-"         gorm:"index"`
+	Username     string         `json:"username"  gorm:"type:varchar(100);uniqueIndex;not null"`
+	PasswordHash string         `json:"-"         gorm:"not null"`
+	Role         Role           `json:"role"      gorm:"default:'user'"`
 }