Tags show up twice under scopes

Happens on CLI, though was first noticed, and most important, on Web due to the all present user prefix.

Was already fully present on the previous deployment but we just completely missed it, e.g.: ourbigbook.com/cirosantilli/physics#physics-education-needs-more-focus-on-understanding-experiments-and-their-history

Minimal CLI example to reproduce:

subdir/asdf.bigb

= asdf

subdir/qwer.bigb

= qwer
{tag=asdf}

Then in the rendering of subdir/qwer.html, the tag asdf appears twice.

The root cause is that scope resolution is finding the same thing twice, one as subdir/asdf and then once again with just asdf (which is then correctly resolved).