전역 구조 리팩터링 및 테스트 확장

lib/features/login/presentation/pages/login_page.dart

@@ -15,6 +15,8 @@ class _LoginPageState extends State<LoginPage> {
   final idController = TextEditingController();
   final passwordController = TextEditingController();
   bool rememberMe = false;
+  bool isLoading = false;
+  String? errorMessage;
 
   @override
   void dispose() {
@@ -23,7 +25,35 @@ class _LoginPageState extends State<LoginPage> {
     super.dispose();
   }
 
-  void _handleSubmit() {
+  Future<void> _handleSubmit() async {
+    if (isLoading) return;
+    setState(() {
+      errorMessage = null;
+      isLoading = true;
+    });
+
+    final id = idController.text.trim();
+    final password = passwordController.text.trim();
+
+    await Future<void>.delayed(const Duration(milliseconds: 600));
+
+    if (id.isEmpty || password.isEmpty) {
+      setState(() {
+        errorMessage = '아이디와 비밀번호를 모두 입력하세요.';
+        isLoading = false;
+      });
+      return;
+    }
+
+    if (password.length < 6) {
+      setState(() {
+        errorMessage = '비밀번호는 6자 이상이어야 합니다.';
+        isLoading = false;
+      });
+      return;
+    }
+
+    if (!mounted) return;
     context.go(dashboardRoutePath);
   }
 
@@ -73,9 +103,33 @@ class _LoginPageState extends State<LoginPage> {
                     ],
                   ),
                   const SizedBox(height: 24),
+                  if (errorMessage != null)
+                    Padding(
+                      padding: const EdgeInsets.only(bottom: 12),
+                      child: Text(
+                        errorMessage!,
+                        style: theme.textTheme.small.copyWith(
+                          color: theme.colorScheme.destructive,
+                        ),
+                      ),
+                    ),
                   ShadButton(
-                    onPressed: _handleSubmit,
-                    child: const Text('로그인'),
+                    onPressed: isLoading ? null : _handleSubmit,
+                    child: Row(
+                      mainAxisAlignment: MainAxisAlignment.center,
+                      mainAxisSize: MainAxisSize.min,
+                      children: [
+                        if (isLoading) ...[
+                          const SizedBox(
+                            width: 16,
+                            height: 16,
+                            child: CircularProgressIndicator(strokeWidth: 2),
+                          ),
+                          const SizedBox(width: 8),
+                        ],
+                        const Text('로그인'),
+                      ],
+                    ),
                   ),
                 ],
               ),