style(theme): 客户端切换深色视觉风格

lib/core/widgets/remote_image.dart

@@ -16,7 +16,7 @@ class RemoteImage extends StatelessWidget {
     this.showFallbackIcon = false,
     this.fallbackIconKey,
     this.fallbackAspectRatio,
-    this.fallbackColor = AppColors.bar,
+    this.fallbackColor = AppColors.raised,
   });
 
   final String path;