v0.0.36 | Upbit API 자격증명 관리 기능 추가

- CustomUser 모델에 Upbit access/secret key 암호화 필드 추가
- UpbitCredentialsView: 자격증명 저장/조회(마스킹)/삭제 API
- UpbitSecretKeyView: 복호화된 키 조회 API (내부 서비스 호출용)
- 마이그레이션 파일 추가

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

users/models.py

@@ -141,6 +141,10 @@ class CustomUser(AbstractBaseUser, PermissionsMixin):
     social_id = models.CharField(max_length=255, blank=True, null=True, verbose_name="소셜 고유 ID")
     profile_image = models.URLField(max_length=500, blank=True, null=True, verbose_name="프로필 이미지 URL")
 
+    # 📈 Upbit API 자격증명 필드
+    encrypted_upbit_access_key = models.BinaryField(blank=True, null=True, verbose_name="Upbit Access Key (암호화)")
+    encrypted_upbit_secret_key = models.BinaryField(blank=True, null=True, verbose_name="Upbit Secret Key (암호화)")
+
     # ☁️ NHN Cloud 자격증명 필드
     nhn_tenant_id = models.CharField(max_length=64, blank=True, null=True, verbose_name="NHN Cloud Tenant ID")
     nhn_username = models.EmailField(blank=True, null=True, verbose_name="NHN Cloud Username")
@@ -218,6 +222,38 @@ class CustomUser(AbstractBaseUser, PermissionsMixin):
             'nhn_tenant_id', 'nhn_username', 'encrypted_nhn_api_password', 'nhn_storage_account'
         ])
 
+    # 📈 Upbit API 키 암복호화
+    def encrypt_upbit_key(self, key: str) -> bytes:
+        """Upbit API 키 암호화"""
+        cipher = Fernet(self.get_encryption_key())
+        return cipher.encrypt(key.encode())
+
+    def decrypt_upbit_access_key(self) -> str:
+        """Upbit Access Key 복호화"""
+        if self.encrypted_upbit_access_key:
+            cipher = Fernet(self.get_encryption_key())
+            return cipher.decrypt(self.encrypted_upbit_access_key).decode()
+        return ""
+
+    def decrypt_upbit_secret_key(self) -> str:
+        """Upbit Secret Key 복호화"""
+        if self.encrypted_upbit_secret_key:
+            cipher = Fernet(self.get_encryption_key())
+            return cipher.decrypt(self.encrypted_upbit_secret_key).decode()
+        return ""
+
+    def save_upbit_credentials(self, access_key: str, secret_key: str):
+        """Upbit API 자격증명 저장"""
+        self.encrypted_upbit_access_key = self.encrypt_upbit_key(access_key)
+        self.encrypted_upbit_secret_key = self.encrypt_upbit_key(secret_key)
+        self.save(update_fields=['encrypted_upbit_access_key', 'encrypted_upbit_secret_key'])
+
+    def clear_upbit_credentials(self):
+        """Upbit API 자격증명 삭제"""
+        self.encrypted_upbit_access_key = None
+        self.encrypted_upbit_secret_key = None
+        self.save(update_fields=['encrypted_upbit_access_key', 'encrypted_upbit_secret_key'])
+
 
 # ============================================
 # NHN Cloud 프로젝트 (멀티 프로젝트 지원)