add no-JS fallback for cart country selector

The delivery country form now has action="/cart/country" with a
noscript submit button. Without JS, changing the country and clicking
Update POSTs to a new CartController.update_country action that saves
the country to session and redirects back to /cart.

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

lib/berrypod_web/components/shop_components/cart.ex

@@ -403,7 +403,8 @@ defmodule BerrypodWeb.ShopComponents.Cart do
       <span class="delivery-line-label">
         Delivery to
         <%= if @available_countries != [] and @mode != :preview do %>
-          <form phx-change="change_country">
+          <form action="/cart/country" method="post" phx-change="change_country">
+            <input type="hidden" name="_csrf_token" value={Phoenix.Controller.get_csrf_token()} />
             <select
               name="country"
               class="delivery-select"
@@ -413,6 +414,9 @@ defmodule BerrypodWeb.ShopComponents.Cart do
                 <option value={code} selected={code == @country_code}>{name}</option>
               <% end %>
             </select>
+            <noscript>
+              <button type="submit" class="themed-button delivery-country-submit">Update</button>
+            </noscript>
           </form>
         <% else %>
           <span>{Berrypod.Shipping.country_name(@country_code)}</span>