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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## 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/lib/audio-utils.ts

@@ -0,0 +1,50 @@
+type RecordAudioType = {
+  (stream: MediaStream): Promise<Blob>
+  stop: () => void
+  currentRecorder?: MediaRecorder
+}
+
+export const recordAudio = (function (): RecordAudioType {
+  const func = async function recordAudio(stream: MediaStream): Promise<Blob> {
+    try {
+      const mediaRecorder = new MediaRecorder(stream, {
+        mimeType: "audio/webm;codecs=opus",
+      })
+      const audioChunks: Blob[] = []
+
+      return new Promise((resolve, reject) => {
+        mediaRecorder.ondataavailable = (event) => {
+          if (event.data.size > 0) {
+            audioChunks.push(event.data)
+          }
+        }
+
+        mediaRecorder.onstop = () => {
+          const audioBlob = new Blob(audioChunks, { type: "audio/webm" })
+          resolve(audioBlob)
+        }
+
+        mediaRecorder.onerror = () => {
+          reject(new Error("MediaRecorder error occurred"))
+        }
+
+        mediaRecorder.start(1000)
+        ;(func as RecordAudioType).currentRecorder = mediaRecorder
+      })
+    } catch (error) {
+      const errorMessage =
+        error instanceof Error ? error.message : "Unknown error occurred"
+      throw new Error("Failed to start recording: " + errorMessage)
+    }
+  }
+
+  ;(func as RecordAudioType).stop = () => {
+    const recorder = (func as RecordAudioType).currentRecorder
+    if (recorder && recorder.state !== "inactive") {
+      recorder.stop()
+    }
+    delete (func as RecordAudioType).currentRecorder
+  }
+
+  return func as RecordAudioType
+})()