Add glue layer: MenuNode replaces MenuItem, remove /internal/menu-items API

- Context processor: get_navigation_tree() replaces get_all_menu_items()
- Menu admin service: MenuItem → MenuNode (container_type/container_id pattern)
- Remove /internal/menu-items endpoint (other apps query menu_nodes directly)
- Remove menu_items relationship from Post model
- Templates: item.post.X → item.X
- Add glue submodule

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

app.py

@@ -24,17 +24,16 @@ async def coop_context() -> dict:
     """
     Coop app context processor.
 
-    - menu_items: direct DB query (coop owns this data)
+    - menu_items: direct DB query via glue layer
     - cart_count/cart_total: fetched from cart internal API
     """
     from shared.infrastructure.context import base_context
-    from bp.menu_items.services.menu_items import get_all_menu_items
+    from glue.services.navigation import get_navigation_tree
     from shared.infrastructure.internal_api import get as api_get
 
     ctx = await base_context()
 
-    # Coop owns menu_items — query directly
-    ctx["menu_items"] = await get_all_menu_items(g.s)
+    ctx["menu_items"] = await get_navigation_tree(g.s)
 
     # Cart data from cart app API
     cart_data = await api_get("cart", "/internal/cart/summary", forward_session=True)