feat: add page_cart_url helper and update shared cart templates for Phase 4

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

suma_browser/templates/_types/cart/_cart.html

@@ -103,7 +103,7 @@
         {% if g.user %}
           <form
             method="post"
-            action="{{ url_for('cart.checkout')|host }}"
+            action="{{ url_for('page_cart.page_checkout')|host if page_post is defined and page_post else url_for('cart_global.checkout')|host }}"
             class="w-full"
           >
             <input type="hidden" name="csrf_token" value="{{ csrf_token() }}">

suma_browser/templates/_types/cart/checkout_error.html

@@ -27,7 +27,7 @@
 
     <div>
       <a
-        href="{{ url_for('cart.view_cart')|host }}"
+        href="{{ cart_url('/') }}"
         class="inline-flex items-center px-3 py-2 text-xs sm:text-sm rounded-full border border-stone-300 bg-white hover:bg-stone-50 transition"
       >
         <i class="fa fa-shopping-cart mr-2" aria-hidden="true"></i>

suma_browser/templates/_types/cart/header/_header.html

@@ -1,7 +1,7 @@
 {% import 'macros/links.html' as links %}
 {% macro header_row(oob=False) %}
   {% call links.menu_row(id='cart-row', oob=oob) %}
-    {% call links.link(url_for('cart.view_cart'), hx_select_search ) %}
+    {% call links.link(cart_url('/'), hx_select_search ) %}
       <i class="fa fa-shopping-cart"></i>
       <h2 class="text-xl font-bold">cart</h2>
     {% endcall %}