Investigate npm pack for offline (i.e. debian) packaging

[fossfreedom]

Building from source on launchpad means no network access - so we cannot use "npm install -g sass" to install the dart-sass stuff needed for the build.

Lets investigate https://stackoverflow.com/questions/23250805/how-to-install-nodejs-project-locally-without-internet-connection

i.e. add the tgz pack file in the debian folder and install via npm install ./debian/...tgz file

Then the build I'm guessing should hopefully work meaning we don't need to ship pre-compiled theme files.