refactor(chat): drop the blur from the block reveal

During a long stream the follow scroll masks the entrance entirely, so
the blur was invisible where it streamed and only a cost risk on weak
GPUs. Keep the compositor-only fade and rise (and the same-tick cascade)
— those are effectively free and still show on short replies where no
scroll motion is involved.

packages/ui/src/index.css

@@ -1378,23 +1378,20 @@ html:not(.dark) .chat-scroll {
   }
 }
 
-/* A block committed mid-stream materializes: fade, a gentle rise, and a
-   touch of blur resolving. Transform and filter are paint-only, so
-   virtualized row measurement is unaffected. Blocks committed in the same
-   tick cascade via --oc-md-enter-delay set inline by the renderer. */
+/* A block committed mid-stream enters with a fade and a gentle rise —
+   compositor-only properties, deliberately nothing heavier: during a long
+   stream the follow scroll masks the entrance anyway, so the effect only
+   really shows on short replies, and those must not pay for a GPU filter.
+   Blocks committed in the same tick cascade via --oc-md-enter-delay set
+   inline by the renderer. */
 @keyframes oc-md-block-enter {
   from {
     opacity: 0;
     transform: translateY(10px);
-    filter: blur(2px);
-  }
-  60% {
-    filter: blur(0);
   }
   to {
     opacity: 1;
     transform: none;
-    filter: none;
   }
 }