Add code to goal title

The same way it's done in UN official SDG pages.

app/components/sdg/goals/show_component.html.erb

@@ -5,7 +5,7 @@
 
   <article class="sdg-goal sdg-goal-<%= goal.code %>">
     <header>
-      <h1><%= goal.title %></h1>
+      <h1><%= heading %></h1>
     </header>
   </article>
 

app/components/sdg/goals/show_component.rb

@@ -15,4 +15,8 @@ class SDG::Goals::ShowComponent < ApplicationComponent
     def processes_feed
       feeds.find { |feed| feed.kind == "processes" }
     end
+
+    def heading
+      safe_join([tag.span(goal.code, class: "goal-code"), tag.span(goal.title, class: "goal-title")], " ")
+    end
 end