Detect orphaned files automatically

[jotaen4tinypilot]

We recently detected orphaned files that weren’t in use for more than a year.

This could easily happen for all asset classes, like .js or .css files, and not just for images.

We could come up with a solution that would report orphaned files during the build. A simple solution I could think of would be to do a full-text search for the paths of all asset files in the code base. That could theoretically create false alerts, but maybe it works sufficiently. (So maybe worth a shot.)