Add cart-mini + auth-menu fragments to all apps, fix like button

- Market, events, federation, account now fetch cart-mini, auth-menu,
  and nav-tree fragments concurrently (matching blog's pattern)
- Move like button template to shared/browser/templates/ so blog can
  find it without needing market's templates in its container

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

account/app.py

@@ -16,14 +16,10 @@ async def account_context() -> dict:
     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
+    from shared.infrastructure.fragments import fetch_fragments
 
     ctx = await base_context()
 
-    ctx["nav_tree_html"] = await fetch_fragment(
-        "blog", "nav-tree",
-        params={"app_name": "account", "path": request.path},
-    )
     # Fallback for _nav.html when nav-tree fragment fetch fails
     ctx["menu_items"] = await get_navigation_tree(g.s)
 
@@ -35,6 +31,23 @@ async def account_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"]
+
+    cart_mini_html, auth_menu_html, nav_tree_html = await fetch_fragments([
+        ("cart", "cart-mini", cart_params or None),
+        ("account", "auth-menu", {"email": user.email} if user else None),
+        ("blog", "nav-tree", {"app_name": "account", "path": request.path}),
+    ])
+    ctx["cart_mini_html"] = cart_mini_html
+    ctx["auth_menu_html"] = auth_menu_html
+    ctx["nav_tree_html"] = nav_tree_html
+
     return ctx