Add Specs section, Reflexive Web essay, fix highlight and dev caching

- Fix highlight() returning SxExpr so syntax-highlighted code renders
  as DOM elements instead of leaking SX source text into the page
- Add Specs section that reads and displays canonical SX spec files
  from shared/sx/ref/ with syntax highlighting
- Add "The Reflexive Web" essay on SX becoming a complete LISP with
  AI as native participant
- Change logo from (<x>) to (<sx>) everywhere
- Unify all backgrounds to bg-stone-100, center code blocks
- Skip component/style cookie cache in dev mode so .sx edits are
  visible immediately on refresh without clearing localStorage

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

sx/sxc/handlers/examples.sx

@@ -235,7 +235,7 @@
         (div :class "p-3 bg-amber-50 rounded text-center"
           (p :class "text-2xl font-bold text-amber-700" "$4.2k")
           (p :class "text-xs text-amber-600" "Revenue")))
-      (div :id "dash-footer" :class "p-3 bg-stone-50 rounded"
+      (div :id "dash-footer" :class "p-3 bg-stone-100 rounded"
         (p :class "text-sm text-stone-500" "Last updated: " now)))))
 
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