Do not call routing helpers before render

Rails' `mounted_helpers` do not work when a component is initialized.
They need to be called when the component is rendered. This change moves
the rendering of tabs from initialization time to render time.

admin/app/components/solidus_admin/ui/pages/index/component.html.erb

@@ -1,12 +1,12 @@
 <%= page do %>
-  <% if @tabs %>
+  <% if tabs %>
     <%= page_header do %>
       <%= render_title %>
     <% end %>
 
     <%= page_header do %>
       <% rendered_tabs = capture do %>
-        <% @tabs.each do %>
+        <% renderable_tabs.each do %>
           <%= render(component("ui/button").new(tag: :a, scheme: :ghost, text: _1.text, 'aria-current': _1.current, href: _1.href)) %>
         <% end %>
       <% end %>

admin/app/components/solidus_admin/ui/pages/index/component.rb

@@ -22,13 +22,18 @@ def columns; []; end
 
   def initialize(page:)
     @page = page
-    @tabs = tabs&.map { |tab| Tab.new(**tab) }
   end
 
   def row_fade(_record)
     false
   end
 
+  def renderable_tabs
+    return unless tabs
+
+    tabs.map { |tab| Tab.new(**tab) }
+  end
+
   def title
     model_class.model_name.human.pluralize
   end