Add cart + auth fragment pre-fetching to blog context

Phase 2 of fragment composition: blog_context() now concurrently
fetches cart-mini and auth-menu HTML fragments from cart and account
apps via fetch_fragments(). Updates shared submodule.

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

app.py

@@ -25,11 +25,13 @@ async def blog_context() -> dict:
 
     - menu_items: via shared.services.navigation
     - cart_count/cart_total: via cart service (shared DB)
+    - cart_mini_html / auth_menu_html: pre-fetched fragments
     """
     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_fragments
 
     ctx = await base_context()
 
@@ -43,6 +45,23 @@ async def blog_context() -> dict:
     ctx["cart_count"] = summary.count + summary.calendar_count + summary.ticket_count
     ctx["cart_total"] = float(summary.total + summary.calendar_total + summary.ticket_total)
 
+    # Pre-fetch cross-app HTML fragments concurrently
+    user = getattr(g, "user", None)
+    cart_params = {}
+    if ident["user_id"] is not None:
+        cart_params["user_id"] = ident["user_id"]
+    if ident["session_id"] is not None:
+        cart_params["session_id"] = ident["session_id"]
+
+    auth_params = {"email": user.email} if user else {}
+
+    cart_mini_html, auth_menu_html = await fetch_fragments([
+        ("cart", "cart-mini", cart_params or None),
+        ("account", "auth-menu", auth_params or None),
+    ])
+    ctx["cart_mini_html"] = cart_mini_html
+    ctx["auth_menu_html"] = auth_menu_html
+
     return ctx