Add OWLS values to non-NC-Mall NC items in Item Getting Guide

Note that there's a known performance issue here: we should try to
fetch all the OWLS values at once, instead of doing them in sequence
while rendering the page!

app/assets/stylesheets/items/sources.sass

@@ -61,6 +61,17 @@
 		text-wrap: balance
 		font-style: italic
 
+	.subtitle
+		font-size: 85%
+		opacity: .85
+
+		a[title]
+			text-decoration-line: underline
+			text-decoration-style: dotted
+
+			&:hover, &:focus
+				text-decoration-style: solid
+
 	/* For wearable items that belong to a specific set that all come together,
 	 * like a Paint Brush. */
 	&[data-group-type="bundle"]

app/helpers/items_helper.rb

@@ -156,6 +156,17 @@ module ItemsHelper
     "Last updated: #{date_str} (#{time_ago_str} ago)"
   end
 
+  def nc_trade_value_subtitle_for(item)
+    value = item.nc_trade_value
+    return nil if value.nil?
+
+    link_to "Owls listing: #{item.nc_trade_value.value_text}",
+      "https://www.neopets.com/~owls",
+      title: 'Owls keeps track of approximate "capsule" values of NC items ' +
+        "for trading. Items with similar values can often be traded for one " +
+        "another. This is an estimate, not a rule!"
+  end
+
   private
 
   def build_on_pet_types(species, special_color=nil, &block)

app/views/items/_item_header.html.haml

@@ -28,7 +28,7 @@
       = link_to t('items.show.resources.jn_items'), jn_items_url_for(item)
       = link_to t('items.show.resources.impress_2020'), impress_2020_url_for(item)
       - if item.nc_trade_value
-        = link_to t('items.show.resources.owls', value: item.nc_trade_value.value_text),
+        = link_to t('items.show.resources.owls', value: item.nc_trade_value_text),
           "https://www.neopets.com/~owls",
           title: nc_trade_value_updated_at_text(item.nc_trade_value)
       - unless item.nc?

app/views/items/_item_list_row.html.haml

@@ -2,5 +2,8 @@
 	%td.thumbnail-cell
 		= link_to item_thumbnail_for(item), item, target: "_blank",
 		  tabindex: "-1"
-	%td.name-cell= link_to item.name, item, target: "_blank"
+	%td.name-cell
+		= link_to item.name, item, target: "_blank"
+		- if subtitle.present?
+			.subtitle= subtitle
 	%td.actions-cell= yield

app/views/items/sources.html.haml

@@ -106,7 +106,7 @@
 				Total: #{pluralize @other_nc_items.size, "item"}
 		%tbody
 			- @other_nc_items.each do |item|
-				= render "item_list_row", item: do
+				= render "item_list_row", item:, subtitle: nc_trade_value_subtitle_for(item) do
 					= button_link_to "NC Trades",
 						item_trades_path(item, type: "offering"),
 						target: "_blank", icon: search_icon