docs(dnsmasq): note auto IP detection is Linux-only, not Docker Desktop

dnsmasq runs in host network mode and auto-detects the host's LAN IP. On
Docker Desktop (Windows/macOS) containers run inside a Linux VM isolated
from the real host LAN, so detection yields the wrong IP and local DNS
resolution does not work. Call this out in the dnsmasq readme and the
in-app deSEC domain notice.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Signed-off-by: Simon L. <szaimen@e.mail.de>

php/templates/includes/desec-domain-notice.twig

@@ -1,2 +1,3 @@
 <p>ℹ️ Your Nextcloud domain (<strong>{{ domain }}</strong>) was registered via deSEC. The <strong>caddy</strong> community container has been automatically enabled as a reverse proxy and the <strong>dnsmasq</strong> container has been automatically enabled so that LAN devices can resolve your Nextcloud domain to the server's local IP address. Please <a target="_blank" href="https://github.com/nextcloud/all-in-one/tree/main/community-containers/dnsmasq"><strong>read the dnsmasq documentation</strong></a> for the required router change.</p>
 <p>⚠️ Caution: if this is a publicly reachable instance, you must disable dnsmasq again as dnsmasq must only run on home servers where port 53 is not publicly exposed.</p>
+<p>⚠️ Note: dnsmasq's automatic local IP address detection only works on a native Linux host. On Docker Desktop (Windows/macOS) it cannot determine the machine's real LAN IP, so local DNS resolution will not work there.</p>