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-platform-2.js

@@ -413,6 +413,14 @@
             "hydrated:", !!islands[j]._sxBoundislandhydrated || !!islands[j]["_sxBound" + "island-hydrated"],
             "children:", islands[j].children.length);
         }
+        // Register popstate handler for back/forward navigation
+        window.addEventListener("popstate", function(e) {
+          var state = e.state;
+          var scrollY = (state && state.scrollY) ? state.scrollY : 0;
+          K.eval("(handle-popstate " + scrollY + ")");
+        });
+        // Signal boot complete
+        document.documentElement.setAttribute("data-sx-ready", "true");
         console.log("[sx] boot done");
       }
     }

shared/static/wasm/sx-platform.js

@@ -413,6 +413,14 @@
             "hydrated:", !!islands[j]._sxBoundislandhydrated || !!islands[j]["_sxBound" + "island-hydrated"],
             "children:", islands[j].children.length);
         }
+        // Register popstate handler for back/forward navigation
+        window.addEventListener("popstate", function(e) {
+          var state = e.state;
+          var scrollY = (state && state.scrollY) ? state.scrollY : 0;
+          K.eval("(handle-popstate " + scrollY + ")");
+        });
+        // Signal boot complete
+        document.documentElement.setAttribute("data-sx-ready", "true");
         console.log("[sx] boot done");
       }
     }

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")