feat: Adding Prompts to admin UI (#3987)

# What does this PR do?

1. Updates Llama Stack Typescript client to include `prompts`api in
playground client.
2. Updates the UI to display prompts and execute basic CRUD operations
for prompts.

(2) adds an explicit "Preview" section when creating the prompt to show
users how the Prompts API behaves as you dynamically edit the prompt
content. See example here:

<p align="center"><img width="468.5" height="333" alt="Screenshot
2025-10-31 at 12 22 34 PM"
src="https://github.com/user-attachments/assets/3542ce7f-56fe-4fb4-b0a3-5cfba5917f6d"
/></p>

Some screen shots:

<details><Summary>Click me to expand!</Summary>

### Prompts List with Prompts
<img width="1906" height="1108" alt="Screenshot 2025-10-31 at 12 20
05 PM"
src="https://github.com/user-attachments/assets/494a4748-ea6a-4527-8cfe-8959cb741c0f"
/>

### Empty Prompts List
<img width="1889" height="1123" alt="Screenshot 2025-10-31 at 12 08
44 PM"
src="https://github.com/user-attachments/assets/ac95b807-d311-4725-86da-0258b3cce81a"
/>

### Create Prompt
<img width="1918" height="1167" alt="Screenshot 2025-10-31 at 11 03
29 AM"
src="https://github.com/user-attachments/assets/b3100a78-f4f3-410f-af89-f7e7fe4a89e7"
/>

### Submit Prompt with error
<img width="1901" height="1213" alt="Screenshot 2025-10-31 at 12 09
28 PM"
src="https://github.com/user-attachments/assets/dca71354-a602-449d-a0d8-0ed3d009a275"
/>
</details>

## Closes https://github.com/llamastack/llama-stack/issues/3322

## Test Plan
Added tests and manual testing.

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

src/llama_stack/ui/components/layout/app-sidebar.tsx

@@ -8,6 +8,7 @@ import {
   MessageCircle,
   Settings2,
   Compass,
+  FileText,
 } from "lucide-react";
 import Link from "next/link";
 import { usePathname } from "next/navigation";
@@ -50,6 +51,11 @@ const manageItems = [
     url: "/logs/vector-stores",
     icon: Database,
   },
+  {
+    title: "Prompts",
+    url: "/prompts",
+    icon: FileText,
+  },
   {
     title: "Documentation",
     url: "https://llama-stack.readthedocs.io/en/latest/references/api_reference/index.html",