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/package.json

@@ -13,13 +13,16 @@
     "test:e2e": "playwright test"
   },
   "dependencies": {
+    "@radix-ui/react-collapsible": "^1.1.11",
     "@radix-ui/react-dialog": "^1.1.13",
     "@radix-ui/react-dropdown-menu": "^2.1.14",
+    "@radix-ui/react-select": "^2.2.5",
     "@radix-ui/react-separator": "^1.1.6",
-    "@radix-ui/react-slot": "^1.2.2",
+    "@radix-ui/react-slot": "^1.2.3",
     "@radix-ui/react-tooltip": "^1.2.6",
     "class-variance-authority": "^0.7.1",
     "clsx": "^2.1.1",
+    "framer-motion": "^11.18.2",
     "llama-stack-client": "0.2.16",
     "lucide-react": "^0.510.0",
     "next": "15.3.3",
@@ -27,6 +30,11 @@
     "next-themes": "^0.4.6",
     "react": "^19.0.0",
     "react-dom": "^19.0.0",
+    "react-markdown": "^10.1.0",
+    "remark-gfm": "^4.0.1",
+    "remeda": "^2.26.1",
+    "shiki": "^1.29.2",
+    "sonner": "^2.0.6",
     "tailwind-merge": "^3.3.0"
   },
   "devDependencies": {