Skip autoinstall confirmation prompt and disable cloud-init post-install

Adds interactive-sections: [] to avoid the "Continue with autoinstall?" prompt,
and disables cloud-init on the installed system to prevent boot delays.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

autoinstall/user-data

@@ -1,6 +1,7 @@
 #cloud-config
 autoinstall:
   version: 1
+  interactive-sections: []
 
   # Locale, keyboard, timezone
   locale: en_US.UTF-8
@@ -102,6 +103,9 @@ autoinstall:
       '
     - curtin in-target --target=/target -- chmod +x /etc/rc.local
 
+    # Disable cloud-init on the installed system (no longer needed after autoinstall)
+    - curtin in-target --target=/target -- touch /etc/cloud/cloud-init.disabled
+
   user-data:
     disable_root: false