Phase 2: Remove dead tree-walk code from eval.sx

eval.sx: 1272 → 846 lines (-33%). sx-browser.js: 392KB → 377KB.

Deleted (superseded by CEK step handlers in cek.sx):
- eval-list: tree-walk dispatch table
- eval-call: tree-walk function dispatch
- sf-if, sf-when, sf-cond (3 variants), sf-case (2 variants)
- sf-and, sf-or, sf-let, sf-begin, sf-quote, sf-quasiquote
- sf-thread-first, sf-set!, sf-define
- ho-map, ho-filter, ho-reduce, ho-some, ho-every, ho-for-each,
  ho-map-indexed, call-fn

Kept (still called by CEK as delegates):
- sf-lambda, sf-defcomp, sf-defisland, sf-defmacro, sf-defstyle,
  sf-deftype, sf-defeffect, sf-letrec, sf-named-let
- sf-scope, sf-provide, sf-dynamic-wind
- expand-macro, qq-expand, cond-scheme?
- call-lambda, call-component, parse-keyword-args
- Strict mode, type helpers

eval-expr is now a stub overridden by CEK fixup.
All tests unchanged: JS 747/747, Full 864/870, Python 679/679.

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

sx/sx/layouts.sx

@@ -70,20 +70,20 @@
              (next-idx (mod (+ idx 1) count))
              (prev-node (nth sibs prev-idx))
              (next-node (nth sibs next-idx)))
-        (div :class "max-w-3xl mx-auto px-4 py-2 grid grid-cols-3 items-center"
+        (div :class "w-full max-w-3xl mx-auto px-4 py-2 grid grid-cols-3 items-center"
              :style (str "opacity:" row-opacity ";transition:opacity 0.3s;")
           (a :href (get prev-node "href")
              :sx-get (get prev-node "href") :sx-target "#main-panel"
              :sx-select "#main-panel" :sx-swap "outerHTML"
              :sx-push-url "true"
-             :class "text-right"
+             :class "text-right min-w-0 truncate"
              :style (tw "text-stone-500 text-sm")
-            (str "← " (get prev-node "label")))
+            (str "\u2190 " (get prev-node "label")))
           (a :href (get node "href")
              :sx-get (get node "href") :sx-target "#main-panel"
              :sx-select "#main-panel" :sx-swap "outerHTML"
              :sx-push-url "true"
-             :class "text-center px-4"
+             :class "text-center min-w-0 truncate px-1"
              :style (if is-leaf
                       (tw "text-violet-700 text-2xl font-bold")
                       (tw "text-violet-700 text-lg font-semibold"))
@@ -92,9 +92,9 @@
              :sx-get (get next-node "href") :sx-target "#main-panel"
              :sx-select "#main-panel" :sx-swap "outerHTML"
              :sx-push-url "true"
-             :class "text-left"
+             :class "text-left min-w-0 truncate"
              :style (tw "text-stone-500 text-sm")
-            (str (get next-node "label") " →")))))))
+            (str (get next-node "label") " \u2192")))))))
 
 ;; Children links — shown as clearly clickable buttons.
 (defcomp ~layouts/nav-children (&key items)