feat(UI): adding MVP playground UI (#2828)

# What does this PR do?
I've been tinkering a little with a simple chat playground in the UI, so
I'm opening the PR with what's kind of a WIP.

If you look at the first commit, that includes the big part of the
changes. The rest of the files changed come from adding installing the
`shadcn` components.

Note this is missing a lot; e.g.,
- sessions
- document upload
- audio (the shadcn components install these by default from
https://shadcn-chatbot-kit.vercel.app/docs/components/chat)

I still need to wire up a lot more to make it actually fully functional
but it does basic chat using the LS Typescript Client.

Basic demo: 

<img width="1329" height="1430" alt="Image"
src="https://github.com/user-attachments/assets/917a2096-36d4-4925-b83b-f1f2cda98698"
/>

<img width="1319" height="1424" alt="Image"
src="https://github.com/user-attachments/assets/fab1583b-1c72-4bf3-baf2-405aee13c6bb"
/>


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<!-- Closes #[issue-number] -->

## Test Plan
<!-- Describe the tests you ran to verify your changes with result
summaries. *Provide clear instructions so the plan can be easily
re-executed.* -->

---------

Signed-off-by: Francisco Javier Arceo <farceo@redhat.com>

llama_stack/ui/components/ui/copy-button.tsx

@@ -0,0 +1,44 @@
+"use client"
+
+import { Check, Copy } from "lucide-react"
+
+import { cn } from "@/lib/utils"
+import { useCopyToClipboard } from "@/hooks/use-copy-to-clipboard"
+import { Button } from "@/components/ui/button"
+
+type CopyButtonProps = {
+  content: string
+  copyMessage?: string
+}
+
+export function CopyButton({ content, copyMessage }: CopyButtonProps) {
+  const { isCopied, handleCopy } = useCopyToClipboard({
+    text: content,
+    copyMessage,
+  })
+
+  return (
+    <Button
+      variant="ghost"
+      size="icon"
+      className="relative h-6 w-6"
+      aria-label="Copy to clipboard"
+      onClick={handleCopy}
+    >
+      <div className="absolute inset-0 flex items-center justify-center">
+        <Check
+          className={cn(
+            "h-4 w-4 transition-transform ease-in-out",
+            isCopied ? "scale-100" : "scale-0"
+          )}
+        />
+      </div>
+      <Copy
+        className={cn(
+          "h-4 w-4 transition-transform ease-in-out",
+          isCopied ? "scale-0" : "scale-100"
+        )}
+      />
+    </Button>
+  )
+}