add external link UX: icons, rel attributes, screen reader labels

New external_link component in core_components handles target="_blank",
rel="noopener noreferrer", external-link icon, and sr-only "(opens in
new tab)" text. Migrated admin providers form, settings (Stripe),
order tracking, onboarding setup links to use it. Fixed rel="noopener"
to "noopener noreferrer" on remaining links (email settings, product
show, core_components card radio). Added sr-only text to shop social
link cards and aria-label to page renderer tracking link.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

lib/berrypod_web/components/core_components.ex

@@ -423,6 +423,25 @@ defmodule BerrypodWeb.CoreComponents do
     """
   end
 
+  @doc """
+  Renders a link to an external site with proper security attributes,
+  an external-link icon, and screen reader context.
+  """
+  attr :href, :string, required: true
+  attr :class, :string, default: nil
+  attr :rest, :global
+  slot :inner_block, required: true
+
+  def external_link(assigns) do
+    ~H"""
+    <a href={@href} target="_blank" rel="noopener noreferrer" class={@class} {@rest}>
+      {render_slot(@inner_block)}
+      <.icon name="hero-arrow-top-right-on-square" class="external-link-icon" />
+      <span class="sr-only">(opens in new tab)</span>
+    </a>
+    """
+  end
+
   ## JS Commands
 
   def show(js \\ %JS{}, selector) do
@@ -608,9 +627,10 @@ defmodule BerrypodWeb.CoreComponents do
       :if={@option[:url]}
       href={@option.url}
       target="_blank"
-      rel="noopener"
+      rel="noopener noreferrer"
       class="card-radio-link"
       onclick="event.stopPropagation();"
+      aria-label={@option.name <> " (opens in new tab)"}
     >
       {@option.name} &nearr;
     </a>

lib/berrypod_web/components/shop_components/content.ex

@@ -431,6 +431,7 @@ defmodule BerrypodWeb.ShopComponents.Content do
               <.social_icon platform={link.platform} />
             </span>
             <span>{link.label}</span>
+            <span class="sr-only">(opens in new tab)</span>
           </a>
         <% end %>
       </div>