Animate orders out with a CSS transition instead of the View Transitions API

The prior attempt wrapped the sign-out router.invalidate() in
document.startViewTransition(), but that had two problems: invalidate()
does its own network refetch inside the transition's update callback,
which freezes the page for the round-trip instead of animating
anything, and TanStack Router's invalidate() explicitly opts itself out
of view transitions (sets shouldViewTransition = false) for exactly
that reason. On top of that, OrdersRoute briefly returns null between
the account loader clearing and the guest-orders lookup resolving,
unmounting OrdersListView and wiping any exit-animation state anyway.

Replace it with a plain, self-contained approach:
- OrdersRoute now keeps rendering the last known non-null orders list
  through that brief gap (a lastKnownOrders ref) instead of unmounting
  OrdersListView, so its local animation state survives.
- OrdersListView holds onto the previous non-empty list for
  EXIT_DURATION_MS after it goes empty, applying an `orderExiting`
  class that fades/slides each card out via a plain CSS transition,
  then swaps to the actual empty state once the transition finishes.

This has no dependency on browser view-transition support, network
timing, or router internals.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/components/orders/OrdersListView.module.scss

@@ -71,13 +71,21 @@
   background: $color-surface;
   color: inherit;
   text-decoration: none;
-  transition: border-color 0.15s ease;
+  transition:
+    border-color 0.15s ease,
+    opacity 0.28s ease,
+    transform 0.28s ease;
 
   &:hover {
     border-color: $color-primary;
   }
 }
 
+.orderExiting .order {
+  opacity: 0;
+  transform: translateY(-8px) scale(0.98);
+}
+
 .orderHeader {
   display: flex;
   justify-content: space-between;