README: link the demo page

klarbild-demo.heidrich-digital.de runs this repository's printlayout.ts and
paper.ts in the browser, so the sheet it lays out is this engine's arithmetic
rather than a mock-up.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Nh4A79bbqT9dcd2inzYUdg

README.md

@@ -16,6 +16,10 @@ Telegram bot. **All of that is optional.** The default install is the print stud
 a database, and nothing else — no API key, no model, no object store, no account
 anywhere.
 
+**[Lay out a sheet in your browser →](https://klarbild-demo.heidrich-digital.de)** — the demo
+page runs this repository's own layout engine client-side and hands you the PDF. No account,
+nothing uploaded.
+
 ```bash
 git clone https://github.com/tillheidrich/klarbild.git && cd klarbild
 cp .env.example .env          # fill in three secrets, the file says which
@@ -144,6 +148,9 @@ the two tools worth knowing.
 
 ## Contributing
 
+[klarbild-demo.heidrich-digital.de](https://klarbild-demo.heidrich-digital.de) is the product
+page; its source is [klarbild-demo](https://git.heidrich-digital.de/till/klarbild-demo).
+
 Issues and pull requests are welcome — see [CONTRIBUTING.md](CONTRIBUTING.md) for
 how the code is laid out and what the house style is. Security reports go to the
 address in [SECURITY.md](SECURITY.md), not to the issue tracker.