XDG_RUNTIME_DIR needs to be set. If it is not set by a user-defined
config, it should default to `/run/user/$UID`

Gracefully handle prefix paths that don't exist, representing them as
directories so they can be escaped from.

Also removes the ".." file info from the backend, instead only creating
it on the frontend

The old effect wasn't running on every data change, since it depended on
table, which is a ref. Now, it will always run on any data change and as
a Layout Effect so it will run before paint.

A bug in sysinfo made it so the initial data would load but not update
until refreshed. This updates the subscription handler with the correct
addContinuousData function to correct this.