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/chat-playground/interrupt-prompt.tsx

@@ -0,0 +1,41 @@
+"use client"
+
+import { AnimatePresence, motion } from "framer-motion"
+import { X } from "lucide-react"
+
+interface InterruptPromptProps {
+  isOpen: boolean
+  close: () => void
+}
+
+export function InterruptPrompt({ isOpen, close }: InterruptPromptProps) {
+  return (
+    <AnimatePresence>
+      {isOpen && (
+        <motion.div
+          initial={{ top: 0, filter: "blur(5px)" }}
+          animate={{
+            top: -40,
+            filter: "blur(0px)",
+            transition: {
+              type: "spring",
+              filter: { type: "tween" },
+            },
+          }}
+          exit={{ top: 0, filter: "blur(5px)" }}
+          className="absolute left-1/2 flex -translate-x-1/2 overflow-hidden whitespace-nowrap rounded-full border bg-background py-1 text-center text-sm text-muted-foreground"
+        >
+          <span className="ml-2.5">Press Enter again to interrupt</span>
+          <button
+            className="ml-1 mr-2.5 flex items-center"
+            type="button"
+            onClick={close}
+            aria-label="Close"
+          >
+            <X className="h-3 w-3" />
+          </button>
+        </motion.div>
+      )}
+    </AnimatePresence>
+  )
+}