docs(readme): embed demo screenshots (hero playground + Lightbox + Modal)

Session-Id: 481d7b9c

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

README.md

@@ -4,6 +4,17 @@ A fork of [vercel-labs/json-render](https://github.com/vercel-labs/json-render)
 
 **🔴 Live demo:** https://jsonrender-demo.oivo.com/playground — type a sentence (e.g. *"landing page for a coffee shop with a photo gallery and a sign-up button"*) and watch a UI build from the JSON spec.
 
+![json-render playground: one sentence becomes a working UI](docs/demo.jpg)
+
+<sub>One sentence → a full landing page. JSON spec on the left, live preview (real-photo gallery + pricing cards) on the right.</sub>
+
+<table>
+<tr>
+<td width="50%"><img src="docs/demo-lightbox.jpg" alt="Lightbox component"/><br/><sub><b>Lightbox</b> — click a thumbnail → fullscreen, prev/next, Esc to close</sub></td>
+<td width="50%"><img src="docs/demo-modal.jpg" alt="Modal component"/><br/><sub><b>Modal</b> — click a button → centered popup form, Esc / backdrop / ✕ to close</sub></td>
+</tr>
+</table>
+
 ## What this fork adds
 
 - **`Image` takes a real `src`** — renders an actual `<img>` (object-cover) when given a URL; falls back to a placeholder otherwise. Galleries use `https://picsum.photos/seed/<word>/<w>/<h>`.