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>

web/adapter-dom.sx

@@ -920,17 +920,12 @@
         (dict "i" 0 "skip" false)
         args)
       (let
-        ((existing (when (and (client?) lake-id) (let ((el (dom-query (str "[data-sx-lake=\"" lake-id "\"]:not([data-sx-lake-claimed])")))) (when el (dom-set-attr el "data-sx-lake-claimed" "1")) el))))
-        (if
-          existing
-          existing
-          (let
-            ((el (dom-create-element lake-tag nil)))
-            (dom-set-attr el "data-sx-lake" (or lake-id ""))
-            (for-each
-              (fn (c) (dom-append el (render-to-dom c env ns)))
-              children)
-            el))))))
+        ((el (dom-create-element lake-tag nil)))
+        (dom-set-attr el "data-sx-lake" (or lake-id ""))
+        (for-each
+          (fn (c) (dom-append el (render-to-dom c env ns)))
+          children)
+        el))))
 
 (define
   render-dom-marsh