feat: show flake options on 'options' tab

[raboof]

we already index the module options for modules provided by 3rd-party flakes (e.g. https://search.nixos.org/flakes?channel=25.11&query=omeka&type=options). I wonder if we should also show these on the 'Options' page, as a 4th category? @KiaraGrouwstra WDYT?

[KiaraGrouwstra]

sounds a bit like nuschtos search maybe. i'd say sooner or later we'll wanna gobble up noogle, nuschtos search, if not more, yeah. :)