Improve parsing fits:blue-acara filter

Previously, passing in `fits:blue` would cause a crash, because
`species_name` part of the split would be `nil`, oops!

In this change, we use a regex for more explicitness about the pattern
we're trying to match. We'll also add more cases next! (You'll note the
error message mentions `fits:nostalgic-faerie-draik`, which isn't
actually possible yet, but will be!)

app/models/item/search/query.rb

@@ -62,11 +62,17 @@ class Item
         when 'restricts'
           is_positive ? Filter.restricts(value) : Filter.not_restricts(value)
         when 'fits'
-          color_name, species_name = value.split("-")
+          match = value.match(/^([^-]+)-([^-]+)$/)
+          if match.present?
+            color_name, species_name = match.captures
             pet_type = load_pet_type_by_name(color_name, species_name)
-          is_positive ?
+            return is_positive ?
               Filter.fits_pet_type(pet_type, color_name:, species_name:) :
               Filter.not_fits_pet_type(pet_type, color_name:, species_name:)
+          end
+          message = I18n.translate('items.search.errors.not_found.fits_target',
+            value: value)
+          raise Item::Search::Error, message
         when 'species'
           begin
             species = Species.find_by_name!(value)

config/locales/en.yml

@@ -361,6 +361,8 @@ en:
           alt_style: We have no record of the "%{filter_text}" alt style. Is it
             spelled correctly?
           pet_type_id: We have no record of pet type %{id}. Weird.
+          fits_target: I'm not sure what "fits:%{value}" means. You can
+            use "fits:blue-acara", "fits:nostalgic-faerie-draik", or similar!
         not_logged_in: The "user" filters are only available if you're logged in.
       flag_keywords:
         is: is