Wrap multiple artifact chips instead of overflowing horizontally

An assistant message with several produced artifacts rendered one chip each in a
non-wrapping flex row, so 3+ chips overflowed and the bubble showed a horizontal
scrollbar. Add flex-wrap + gap-y-2 (the existing per-chip mr-2 keeps the
horizontal spacing) so the chips wrap to the next line, matching the other
artifact-chip render branch.

frontend/src/conversation/ConversationBubble.tsx

@@ -691,7 +691,7 @@ const ConversationBubble = forwardRef<
           </div>
         )}
         {message && (
-          <div className="my-2 ml-2 flex justify-start">
+          <div className="my-2 ml-2 flex flex-wrap justify-start gap-y-2">
             {type === 'ERROR' ? (
               <div className="relative mr-2 block items-center justify-center">
                 <div>{retryBtn}</div>