fix(ui): 保留空态既有字号口径

lib/core/theme/app_dimens.dart

@@ -17,6 +17,8 @@ abstract final class AppDimens {
   static const double pillRadius = 20;
 
   static const double caption = 12;
+  static const double emptyStateSubtitle = 12.5;
+  static const double emptyStateAction = 13;
   static const double body = 14;
   static const double listTitle = 15;
   static const double sectionTitle = 16;

lib/core/widgets/empty_state.dart

@@ -140,7 +140,7 @@ class _EmptyCopy extends StatelessWidget {
               textAlign: TextAlign.center,
               style: const TextStyle(
                 color: AppColors.muted,
-                fontSize: AppDimens.caption,
+                fontSize: AppDimens.emptyStateSubtitle,
                 height: 1.45,
               ),
             ),
@@ -158,7 +158,7 @@ class _EmptyCopy extends StatelessWidget {
             ),
             child: Text(
               actionLabel!,
-              style: const TextStyle(fontSize: AppDimens.body),
+              style: const TextStyle(fontSize: AppDimens.emptyStateAction),
             ),
           ),
         ],