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/hooks/use-audio-recording.ts

@@ -0,0 +1,93 @@
+import { useEffect, useRef, useState } from "react"
+
+import { recordAudio } from "@/lib/audio-utils"
+
+interface UseAudioRecordingOptions {
+  transcribeAudio?: (blob: Blob) => Promise<string>
+  onTranscriptionComplete?: (text: string) => void
+}
+
+export function useAudioRecording({
+  transcribeAudio,
+  onTranscriptionComplete,
+}: UseAudioRecordingOptions) {
+  const [isListening, setIsListening] = useState(false)
+  const [isSpeechSupported, setIsSpeechSupported] = useState(!!transcribeAudio)
+  const [isRecording, setIsRecording] = useState(false)
+  const [isTranscribing, setIsTranscribing] = useState(false)
+  const [audioStream, setAudioStream] = useState<MediaStream | null>(null)
+  const activeRecordingRef = useRef<any>(null)
+
+  useEffect(() => {
+    const checkSpeechSupport = async () => {
+      const hasMediaDevices = !!(
+        navigator.mediaDevices && navigator.mediaDevices.getUserMedia
+      )
+      setIsSpeechSupported(hasMediaDevices && !!transcribeAudio)
+    }
+
+    checkSpeechSupport()
+  }, [transcribeAudio])
+
+  const stopRecording = async () => {
+    setIsRecording(false)
+    setIsTranscribing(true)
+    try {
+      // First stop the recording to get the final blob
+      recordAudio.stop()
+      // Wait for the recording promise to resolve with the final blob
+      const recording = await activeRecordingRef.current
+      if (transcribeAudio) {
+        const text = await transcribeAudio(recording)
+        onTranscriptionComplete?.(text)
+      }
+    } catch (error) {
+      console.error("Error transcribing audio:", error)
+    } finally {
+      setIsTranscribing(false)
+      setIsListening(false)
+      if (audioStream) {
+        audioStream.getTracks().forEach((track) => track.stop())
+        setAudioStream(null)
+      }
+      activeRecordingRef.current = null
+    }
+  }
+
+  const toggleListening = async () => {
+    if (!isListening) {
+      try {
+        setIsListening(true)
+        setIsRecording(true)
+        // Get audio stream first
+        const stream = await navigator.mediaDevices.getUserMedia({
+          audio: true,
+        })
+        setAudioStream(stream)
+
+        // Start recording with the stream
+        activeRecordingRef.current = recordAudio(stream)
+      } catch (error) {
+        console.error("Error recording audio:", error)
+        setIsListening(false)
+        setIsRecording(false)
+        if (audioStream) {
+          audioStream.getTracks().forEach((track) => track.stop())
+          setAudioStream(null)
+        }
+      }
+    } else {
+      await stopRecording()
+    }
+  }
+
+  return {
+    isListening,
+    isSpeechSupported,
+    isRecording,
+    isTranscribing,
+    audioStream,
+    toggleListening,
+    stopRecording,
+  }
+}