This commit removes the need for a custom Opaleye fork by relying on
a newly-created `opaleye-textsearch` package following the design
outlined here:

https://github.com/tomjaguarpaw/haskell-opaleye/pull/563#issuecomment-1782794439

In my previous commit I had changed their implementation to use the
FromJSON/ToJSON istances, making sure those were backward compatible,
but apparently that wasn't the case.

After Fabien's changes, this needed amendment.

Also, fixed breadcrumbs to accept AppRoute.

Otherwise, if doc wasn't visited yet, codimd returns some large HTML
page.