After some more debugging I found that the redirection loop is not caused by the apache rewrite rules but by /var/www/fog/api/index.php and those included by that PHP file. Maybe this is because we don’t supply correct parameters?! Would be nice if it wouldn’t redirect in an endless loop.
@Dino_Nerd I think you can re-add the RewriteRule ^/(.*)$ /fog/api/index.php [QSA,L] in your 001-fog.conf and still should be able to access and boot http://192.168.0.143/pmagic/bzImage64 if that folder is in /var/www!!
Note to myself: Accessing directories (like http://192.168.0.143/pmagic/) does not work albeit the second RewriteCond because DirectoryIndex setting makes it request index.html in that directory, which usually does not exist. Therefore again redirecting it to /fog/api/index.php