Fetch nav-tree fragment from blog, drop local menu_items query

Navigation is now rendered by blog as an HTML fragment. This app
fetches it with its own app_name and path for correct highlighting.

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

app.py

@@ -4,7 +4,7 @@ import path_setup  # noqa: F401  # adds shared/ to sys.path
 from decimal import Decimal
 from pathlib import Path
 
-from quart import g, abort
+from quart import g, abort, request
 from jinja2 import FileSystemLoader, ChoiceLoader
 from sqlalchemy import select
 
@@ -45,16 +45,21 @@ async def cart_context() -> dict:
     - cart / calendar_cart_entries / total / calendar_total: direct DB
       (cart app owns this data)
     - cart_count: derived from cart + calendar entries (for _mini.html)
-    - menu_items: via shared.services.navigation
+    - nav_tree_html: fetched from blog as fragment
 
     When g.page_post exists, cart and calendar_cart_entries are page-scoped.
     Global cart_count / cart_total stay global for cart-mini.
     """
     from shared.infrastructure.context import base_context
-    from shared.services.navigation import get_navigation_tree
+    from shared.infrastructure.fragments import fetch_fragment
 
     ctx = await base_context()
 
+    ctx["nav_tree_html"] = await fetch_fragment(
+        "blog", "nav-tree",
+        params={"app_name": "cart", "path": request.path},
+    )
+
     # Cart app owns cart data — use g.cart from _load_cart
     all_cart = getattr(g, "cart", None) or []
     all_cal = await get_calendar_cart_entries(g.s)
@@ -86,8 +91,6 @@ async def cart_context() -> dict:
     ctx["calendar_total"] = calendar_total
     ctx["ticket_total"] = ticket_total
 
-    ctx["menu_items"] = await get_navigation_tree(g.s)
-
     return ctx