Add a view-and-evaluate license

All rights reserved: the code may be read, and run unmodified for private
evaluation; nothing else.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

README.md

@@ -107,3 +107,8 @@ python -m app.web                                    # http://127.0.0.1:5000
   invoice number prefix, colour theme) and their rooms (`room`) are set up directly in the database; everything
   else is entered in the app. Logos and photos for the invoice header go into `app/static/invoice/`, named in
   `unit.logo` / `unit.photo`.
+
+## License
+
+All rights reserved. This is not open-source software: the code is published to be read, and to be run
+unmodified for your own private evaluation — nothing else. See [LICENSE](LICENSE).