README: replace vague cross-app section with actual code dependencies

List specific model imports, glue services, and internal APIs
that market code actually references.

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

README.md

@@ -43,11 +43,16 @@ shared/                 # Submodule → git.rose-ash.com/coop/shared.git
 glue/                   # Submodule → git.rose-ash.com/coop/glue.git
 ```
 
-## Cross-App Integration
+## Dependencies
 
-- **Cart:** "Add to cart" posts to cart app. Cart widget fetched via internal API.
-- **Blog:** Post/page data fetched via internal API for page-scoped marketplaces.
-- **Glue:** MarketPlace uses generic containers (`container_type + container_id`) to attach to pages without FK coupling.
+**Cross-app model imports:**
+- `blog.models.ghost_content.Post` — `app.py` hydrates page data for marketplace views
+
+**Glue services:**
+- `glue.services.navigation.get_navigation_tree` — context processor builds site nav
+
+**Internal APIs:**
+- Calls `GET /internal/cart/summary` — context processor for cart widget
 
 ## Scraping