Revert render-dom-lake child re-rendering — broke stepper preview

The change to re-render children when non-empty caused the stepper's
lake to show raw SX again (the ~tw expressions in steps-to-preview
were rendered as text). Reverted to the simpler approach: reuse the
existing SSR element and preserve its content entirely.

The copyright route not updating during SPA nav is a pre-existing
issue (path is an island parameter, not a reactive signal).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

shared/static/wasm/sx/boot.sx

@@ -440,7 +440,7 @@
           (e)
           (let
             ((state (host-get e "state"))
-              (scrollY (if state (or (dict-get state "scrollY") 0) 0)))
+              (scrollY (if state (or (get state "scrollY") 0) 0)))
             (handle-popstate scrollY))))
       (dom-set-attr
         (host-get (dom-document) "documentElement")