fix assistant streaming scroll lock

apps/nextjs/src/components/assistant/assistant-panel.module.css

@@ -330,7 +330,6 @@
   flex: 1;
   flex-direction: column;
   overflow-y: auto;
-  scroll-behavior: smooth;
 }
 
 .messages {
@@ -1313,8 +1312,4 @@
     animation: none;
     transition: none;
   }
-
-  .viewport {
-    scroll-behavior: auto;
-  }
 }