fix: Include copyleft icon in footer copy

There are several assets in the footer which should be properly implemented as SVGs. Not all of them were included in the source Figma design files as SVGs, meaning that not all of them could be extracted as SVG. The copyleft icon, however, which is missing entirely from the current build, was included as an SVG, and so should not only be stubbed out with "for production only" assets like the social media icons are currently, it should be fully implemented as an SVG.

This check-in addresses that, adding the aforementioned SVG and a little dash of SASS to get it to display as an icon and to align with the text baseline of the line it's on.

Closes: #29 (closed)