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/pages/docs.sx

@@ -240,4 +240,42 @@
     "tail-call-optimization" (~essay-tail-call-optimization)
     "continuations" (~essay-continuations)
     "godel-escher-bach" (~essay-godel-escher-bach)
+    "reflexive-web" (~essay-reflexive-web)
     :else (~essay-sx-sucks)))
+
+;; ---------------------------------------------------------------------------
+;; Specs section
+;; ---------------------------------------------------------------------------
+
+(defpage specs-index
+  :path "/specs/"
+  :auth :public
+  :layout (:sx-section
+    :section "Specs"
+    :sub-label "Specs"
+    :sub-href "/specs/core"
+    :sub-nav (~section-nav :items specs-nav-items :current "Core")
+    :selected "Core")
+  :data (spec-data "core")
+  :content (~spec-core-content :spec-files spec-files))
+
+(defpage specs-page
+  :path "/specs/<slug>"
+  :auth :public
+  :layout (:sx-section
+    :section "Specs"
+    :sub-label "Specs"
+    :sub-href "/specs/core"
+    :sub-nav (~section-nav :items specs-nav-items
+               :current (find-current specs-nav-items slug))
+    :selected (or (find-current specs-nav-items slug) ""))
+  :data (spec-data slug)
+  :content (if spec-not-found
+    (~spec-not-found :slug slug)
+    (case slug
+      "core" (~spec-core-content :spec-files spec-files)
+      :else (~spec-detail-content
+        :spec-title spec-title
+        :spec-desc spec-desc
+        :spec-filename spec-filename
+        :spec-source spec-source))))