I have also tried creating /usr/share/polkit-1/rules.d/49-rootpw_global.rules with the same contents, [...]
The problem with that is simply that the PolicyKit in Debian Unstable/Testing/Stable does not read the _javascript_ rules files.
Only the version using JS-based rules files (in experimental for ages) does that. So you might want to search for a solution using the old configuration syntax here.