feat(storefront): section-based homepages, header action partials, fixes

Phase 1 — Section-based store homepages:
- Store defaults use template="full" with per-platform sections JSON
- OMS: shop hero + features + CTA; Loyalty: rewards hero + features + CTA
- Hosting: services hero + features + CTA
- Deep placeholder resolution for {{store_name}} inside sections JSON
- landing-full.html uses resolved page_sections from context

Phase 2 — Module-contributed header actions:
- header_template field on MenuItemDefinition + DiscoveredMenuItem
- Catalog provides header-search.html partial
- Cart provides header-cart.html partial with badge
- Base template iterates storefront_nav.actions with {% include %}
- Generic icon fallback for actions without a template

Fixes:
- Store theme API: get_store_by_code → get_store_by_code_or_subdomain

Docs:
- CMS redesign proposal: menu restructure, page types, translations UI

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

app/templates/storefront/base.html

@@ -105,36 +105,17 @@
                     {% endfor %}
                 </nav>
 
-                {# Right side actions #}
+                {# Right side actions — module-provided via header_template #}
                 <div class="flex items-center space-x-4">
-
-                    {# Action items from enabled modules (search, cart, etc.) #}
-                    {% set action_ids = storefront_nav.get('actions', [])|map(attribute='id')|list %}
-
-                    {% if 'search' in action_ids %}
-                    {# Search #}
-                    <button @click="openSearch()" class="p-2 rounded-lg hover:bg-gray-100 dark:hover:bg-gray-700">
-                        <svg class="w-5 h-5" fill="none" stroke="currentColor" viewBox="0 0 24 24">
-                            <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2"
-                                  d="M21 21l-6-6m2-5a7 7 0 11-14 0 7 7 0 0114 0z"></path>
-                        </svg>
-                    </button>
-                    {% endif %}
-
-                    {% if 'cart' in action_ids %}
-                    {# Cart #}
-                    <a href="{{ base_url }}cart" class="relative p-2 rounded-lg hover:bg-gray-100 dark:hover:bg-gray-700">
-                        <svg class="w-5 h-5" fill="none" stroke="currentColor" viewBox="0 0 24 24">
-                            <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2"
-                                  d="M3 3h2l.4 2M7 13h10l4-8H5.4M7 13L5.4 5M7 13l-2.293 2.293c-.63.63-.184 1.707.707 1.707H17m0 0a2 2 0 100 4 2 2 0 000-4zm-8 2a2 2 0 11-4 0 2 2 0 014 0z"></path>
-                        </svg>
-                        <span x-show="cartCount > 0"
-                              x-text="cartCount"
-                              class="absolute -top-1 -right-1 bg-accent text-white text-xs rounded-full h-5 w-5 flex items-center justify-center"
-                              style="background-color: var(--color-accent)">
-                        </span>
-                    </a>
-                    {% endif %}{# cart #}
+                    {% for item in storefront_nav.get('actions', []) %}
+                        {% if item.header_template %}
+                            {% include item.header_template %}
+                        {% else %}
+                            <a href="{{ base_url }}{{ item.route }}" class="p-2 rounded-lg hover:bg-gray-100 dark:hover:bg-gray-700" title="{{ _(item.label_key) }}">
+                                <span class="w-5 h-5" x-html="$icon('{{ item.icon }}', 'w-5 h-5')"></span>
+                            </a>
+                        {% endif %}
+                    {% endfor %}
 
                     {# Theme toggle #}
                     <button @click="toggleTheme()"