Restore menu_items fallback for nav, update shared submodule

Keep get_navigation_tree() as fallback when nav-tree fragment fetch
fails. Update shared submodule with fixed app slug URLs in nav.

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

app.py

@@ -18,6 +18,7 @@ from bp import (
 async def federation_context() -> dict:
     """Federation app context processor."""
     from shared.infrastructure.context import base_context
+    from shared.services.navigation import get_navigation_tree
     from shared.infrastructure.cart_identity import current_cart_identity
     from shared.infrastructure.fragments import fetch_fragment
 
@@ -27,6 +28,8 @@ async def federation_context() -> dict:
         "blog", "nav-tree",
         params={"app_name": "federation", "path": request.path},
     )
+    # Fallback for _nav.html when nav-tree fragment fetch fails
+    ctx["menu_items"] = await get_navigation_tree(g.s)
 
     # Cart data (consistent with all other apps)
     ident = current_cart_identity()