chore: move src/llama_stack/ui to src/llama_stack_ui (#4068)

# What does this PR do?
This better separates UI from backend code, which was a point of
confusion often for our beloved AI friends.


## Test Plan
CI

src/llama_stack_ui/app/logs/responses/page.tsx

@@ -0,0 +1,7 @@
+"use client";
+
+import { ResponsesTable } from "@/components/responses/responses-table";
+
+export default function ResponsesPage() {
+  return <ResponsesTable paginationOptions={{ limit: 20 }} />;
+}