일반 사용자 가입 시 External 하드코딩 제거 및 소속 표시 개선

userfront/lib/features/auth/presentation/signup_screen.dart

@@ -316,9 +316,7 @@ class _SignupScreenState extends State<SignupScreen> {
         phone: _phoneController.text.trim(),
         affiliationType: _affiliationType,
         companyCode: _affiliationType == 'AFFILIATE' ? _companyCode : null,
-        department: _deptController.text.trim().isEmpty
-            ? (_affiliationType == 'GENERAL' ? 'External' : '')
-            : _deptController.text.trim(),
+        department: _deptController.text.trim(),
         termsAccepted: true,
       );
       if (mounted) _showSuccessDialog();