Move Item Getting Guide subtitle UI out of helpers, into templates

I thought to myself, "I wonder if it's possible to use a sneaky hacky
`content_for` trick to be able to run this code in the template." And
indeed it is!

It's tricky cuz like, I want to render this template, and I want to
provide _multiple_ slots of content to it. So, in this variant, we keep
the block as being primarily for the actions, but also optionally
accept `content_for :subtitle` inside that block, too.

Executing that correctly is a bit tricky! The subtitle comes *before*
the actions. So, we `yield` the actions block immediately, save it to a
variable, and *then* get the subtitle block.

app/helpers/items_helper.rb

@@ -156,25 +156,6 @@ 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", target: "_blank",
-      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
-
-  def dyeworks_explanation_subtitle_for(item)
-    base_item = item.dyeworks_base_item
-    content_tag :span, class: "dyeworks-explanation" do
-      concat link_to(base_item.name, base_item, target: "_blank")
-      concat " + 1 Potion"
-    end
-  end
-
   def nc_total_for(items)
     items.map(&:current_nc_price).sum
   end

app/views/items/_item_list_row.html.haml

@@ -1,4 +1,6 @@
-- subtitle = nil unless defined? subtitle
+-# Run the block first, so we can get the subtitle content if provided!
+- content = yield
+- subtitle = yield :subtitle
 
 %tr
 	%td.thumbnail-cell
@@ -8,4 +10,4 @@
 		= link_to item.name, item, target: "_blank"
 		- if subtitle.present?
 			.subtitle= subtitle
-	%td.actions-cell= yield
+	%td.actions-cell= content

app/views/items/sources.html.haml

@@ -61,8 +61,12 @@
 					Buy all in NC Mall
 		%tbody
 			- @buyable_dyeworks_items.each do |item|
-				= render "item_list_row", item:,
+				= render "item_list_row", item: do
-					subtitle: dyeworks_explanation_subtitle_for(item) do
+					- base_item = item.dyeworks_base_item
+					- content_for :subtitle, flush: true do
+						%span.dyeworks-explanation
+							= link_to base_item.name, base_item, target: "_blank"
+							+ 1 potion
 					%button{onclick: "alert('Todo!')"}
 						= cart_icon alt: ""
 						Buy base (#{item.dyeworks_base_item.current_nc_price} NC)
@@ -153,7 +157,12 @@
 				Total: #{pluralize @other_nc_items.size, "item"}
 		%tbody
 			- @other_nc_items.each do |item|
-				= render "item_list_row", item:, subtitle: nc_trade_value_subtitle_for(item) do
+				= render "item_list_row", item: do
+					- content_for :subtitle, flush: true do
+						- if item.nc_trade_value.present?
+							= link_to "Owls listing: #{item.nc_trade_value.value_text}",
+								"https://www.neopets.com/~owls", target: "_blank",
+								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!'
 					= button_link_to "NC Trades",
 						item_trades_path(item, type: "offering"),
 						target: "_blank", icon: search_icon