Revert render-dom-lake to original, simplify stepper lake

Reverted render-dom-lake SSR reuse — it broke OOB swaps (claimed
old lake elements during morph, stale content in copyright). The
framework's morphing handles lake updates correctly already.

Stepper: lake passes nil on client (prevents raw SX flash), effect
always calls rebuild-preview (no initial-render flag needed). Server
renders the expression for SSR; client rebuilds via render-to-dom
after boot when ~tw is available.

Removed initial-render dict flag — unnecessary complexity.

Copyright route not updating is a pre-existing issue: render-dom-island
renders the header island inline during OOB content rendering (sets
island-hydrated mark), but the copyright lake content doesn't reflect
the new path. Separate investigation needed.

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

shared/static/wasm/sx/orchestration.sx

@@ -1589,7 +1589,7 @@
           (try-client-route pathname target-sel)
           (browser-scroll-to 0 scrollY)
           (let
-            ((headers (build-request-headers target "GET" url)))
+            ((headers (dict "SX-History-Restore" "true")))
             (fetch-and-restore target url headers scrollY)))))))
 
 (define