docs: add HeroLib Web UI documentation

- Add quick start guide with code example
- List key features of the UI
- Detail built-in tools and their paths

lib/web/ui/README.md

@@ -0,0 +1,28 @@
+# HeroLib Web UI
+
+Modern web UI framework for HeroLib, built with **V** + **Bootstrap 5**.
+
+## Quick Start
+
+```v
+import freeflowuniverse.herolib.web.ui
+
+mut app := ui.new_app()
+app.title = 'My HeroLib App'
+app.start(port: 8080)!
+```
+
+👉 Open [http://localhost:8080/admin](http://localhost:8080/admin)
+
+## Features
+
+* 🎨 Light/Dark themes
+* 🧭 Dynamic menus
+* 📱 Responsive design (Bootstrap 5)
+* ⚡ Fast & lightweight
+
+## Built-in Tools
+
+* **HeroPrompt** → `/admin/heroprompt`
+* **Chat** → `/admin/chat`
+* **HeroScript** → `/admin/heroscript`