Add Unraid deployment setup

docker-compose.unraid.yml bind-mounts data to /mnt/user/appdata/kids-calendar
instead of a named volume, matching Unraid's appdata convention so backup
plugins pick it up. UNRAID.md covers getting the code onto the array,
running via Compose Manager or terminal, reverse-proxy/HTTPS notes, and
updating. Linked from README.

README.md

@@ -38,6 +38,11 @@ Data lives in a named volume (`kids-calendar-data`), so it survives
 container rebuilds. To back it up, back up that volume (or bind-mount
 `./data:/app/data` in `docker-compose.yml` instead and back up that folder).
 
+**Running on Unraid specifically?** See [UNRAID.md](UNRAID.md) — it uses
+`docker-compose.unraid.yml`, which bind-mounts to
+`/mnt/user/appdata/kids-calendar` instead of a named volume, matching
+Unraid's usual appdata convention.
+
 ### Environment variables
 
 | Variable | Default | Notes |