Decouple cart/market DBs: denormalize product data, AP internal inbox, OAuth scraper auth

Remove cross-DB relationships (CartItem.product, CartItem.market_place,
OrderItem.product) that break with per-service databases. Denormalize
product and marketplace fields onto cart_items/order_items at write time.

- Add AP internal inbox infrastructure (shared/infrastructure/internal_inbox*)
  for synchronous inter-service writes via HMAC-authenticated POST
- Cart inbox blueprint handles Add/Remove/Update rose:CartItem activities
- Market app sends AP activities to cart inbox instead of writing CartItem directly
- Cart services use denormalized columns instead of cross-DB hydration/joins
- Add marketplaces-by-ids data endpoint to market service
- Alembic migration adds denormalized columns to cart_items and order_items
- Add OAuth device flow auth to market scraper persist_api (artdag client pattern)

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

cart/templates/_types/order/_items.html

@@ -7,13 +7,13 @@
       <ul class="divide-y divide-stone-100 text-xs sm:text-sm">
         {% for item in order.items %}
           <li>
-            <a class="w-full py-2 flex gap-3" href="{{ market_product_url(item.product.slug) }}">
+            <a class="w-full py-2 flex gap-3" href="{{ market_product_url(item.product_slug) }}">
               {# Thumbnail #}
               <div class="w-12 h-12 sm:w-14 sm:h-14 rounded-md bg-stone-100 flex-shrink-0 overflow-hidden">
-                {% if item.product and item.product.image %}
+                {% if item.product_image %}
                   <img
-                    src="{{ item.product.image }}"
-                    alt="{{ item.product_title or item.product.title or 'Product image' }}"
+                    src="{{ item.product_image }}"
+                    alt="{{ item.product_title or 'Product image' }}"
                     class="w-full h-full object-contain object-center"
                     loading="lazy"
                     decoding="async"
@@ -29,7 +29,7 @@
               <div class="flex-1 flex justify-between gap-3">
                 <div>
                   <p class="font-medium">
-                    {{ item.product_title or (item.product and item.product.title) or 'Unknown product' }}
+                    {{ item.product_title or 'Unknown product' }}
                   </p>
                   <p class="text-[11px] text-stone-500">
                     Product ID: {{ item.product_id }}