Fix orders defpage: length→len primitive, handle _RawHTML in serialize()

- Fix undefined symbol 'length' → use 'len' primitive in orders.sx
- Add _RawHTML handling in serialize() — wraps as (raw! "...") for SX wire format
  instead of falling through to repr() which produced unparseable symbol names

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

orders/sxc/pages/orders.sx

@@ -28,7 +28,7 @@
            :search-headers-desktop "{\"X-Origin\":\"search-desktop\",\"X-Search\":\"true\"}")
   :content (let* ((pfx (route-prefix))
                   (detail-url-raw (str pfx (url-for "defpage_order_detail" :order-id 0)))
-                  (detail-prefix (slice detail-url-raw 0 (- (length detail-url-raw) 2)))
+                  (detail-prefix (slice detail-url-raw 0 (- (len detail-url-raw) 2)))
                   (rows-url (str pfx (url-for "orders.orders_rows"))))
              (~orders-list-content
                :orders orders