라우터 구조 개선 및 리다이렉트 시 파라미터 유실 수정

userfront/lib/core/i18n/locale_utils.dart

@@ -75,14 +75,16 @@ String buildLocalizedPath(String localeCode, Uri uri) {
       restSegments = segments.skip(1);
     }
   }
-  final newSegments = [localeCode, ...restSegments];
-  final path = '/${newSegments.join('/')}';
-  final queryPart = uri.hasQuery ? '?${uri.query}' : '';
-  final fragmentPart = uri.fragment.isNotEmpty ? '#${uri.fragment}' : '';
-  return '$path$queryPart$fragmentPart';
-}
-
-String buildSigninRedirectPath(String localeCode, Uri uri) {
-  final queryPart = uri.hasQuery ? '?${uri.query}' : '';
-  return '/$localeCode/signin$queryPart';
+  final newPath = '/${[localeCode, ...restSegments].join('/')}';
+  
+  // Return only the path and query part to avoid GoRouter confusion with full URLs
+  final newUri = uri.replace(path: newPath);
+  String result = newUri.path;
+  if (newUri.hasQuery) {
+    result += '?${newUri.query}';
+  }
+  if (newUri.hasFragment) {
+    result += '#${newUri.fragment}';
+  }
+  return result;
 }