chore: move src/llama_stack/ui to src/llama_stack_ui

# What does this PR do?


## Test Plan

src/llama_stack_ui/components/responses/items/message-item.tsx

@@ -0,0 +1,41 @@
+import { MessageBlock } from "@/components/chat-playground/message-components";
+import { MessageItem } from "../utils/item-types";
+
+interface MessageItemProps {
+  item: MessageItem;
+  index: number;
+  keyPrefix: string;
+  defaultRole?: string;
+}
+
+export function MessageItemComponent({
+  item,
+  index,
+  keyPrefix,
+  defaultRole = "unknown",
+}: MessageItemProps) {
+  let content = "";
+
+  if (typeof item.content === "string") {
+    content = item.content;
+  } else if (Array.isArray(item.content)) {
+    content = item.content
+      .map(c => {
+        return c.type === "input_text" || c.type === "output_text"
+          ? c.text
+          : JSON.stringify(c);
+      })
+      .join(" ");
+  }
+
+  const role = item.role || defaultRole;
+  const label = role.charAt(0).toUpperCase() + role.slice(1);
+
+  return (
+    <MessageBlock
+      key={`${keyPrefix}-${index}`}
+      label={label}
+      content={content}
+    />
+  );
+}