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

@@ -3,7 +3,7 @@ import path_setup  # noqa: F401  # adds shared/ to sys.path
 
 from pathlib import Path
 
-from quart import g, abort
+from quart import g, abort, request
 from jinja2 import FileSystemLoader, ChoiceLoader
 from sqlalchemy import select
 
@@ -17,20 +17,23 @@ async def market_context() -> dict:
     """
     Market app context processor.
 
-    - menu_items: direct DB query
+    - nav_tree_html: fetched from blog as fragment
     - cart_count/cart_total: via cart service (includes calendar entries)
     - cart: direct ORM query (templates need .product relationship)
     """
     from shared.infrastructure.context import base_context
-    from shared.services.navigation import get_navigation_tree
     from shared.services.registry import services
     from shared.infrastructure.cart_identity import current_cart_identity
+    from shared.infrastructure.fragments import fetch_fragment
     from shared.models.market import CartItem
     from sqlalchemy.orm import selectinload
 
     ctx = await base_context()
 
-    ctx["menu_items"] = await get_navigation_tree(g.s)
+    ctx["nav_tree_html"] = await fetch_fragment(
+        "blog", "nav-tree",
+        params={"app_name": "market", "path": request.path},
+    )
 
     ident = current_cart_identity()