Add Content Addressing page under CEK Machine

Dedicated page documenting and demonstrating content-addressed
computation. How it works, why it matters, the path to IPFS.

Live demo: counter + name widget with CID generation, history,
and restore-from-CID input.

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

shared/sx/ref/platform_js.py

@@ -1481,6 +1481,12 @@ PLATFORM_JS_POST = '''
 
 
 PLATFORM_CEK_JS = '''
+  // String/number utilities needed by transpiled spec code (content-hash etc)
+  PRIMITIVES["char-code-at"] = function(s, i) { return s.charCodeAt(i); };
+  var charCodeAt = PRIMITIVES["char-code-at"];
+  PRIMITIVES["to-hex"] = function(n) { return (n >>> 0).toString(16); };
+  var toHex = PRIMITIVES["to-hex"];
+
   // =========================================================================
   // Platform: CEK module — explicit CEK machine
   // =========================================================================
@@ -1532,10 +1538,6 @@ CEK_FIXUPS_JS = '''
   PRIMITIVES["is-html-tag?"] = function(n) { return HTML_TAGS.indexOf(n) >= 0; };
   PRIMITIVES["make-env"] = function() { return merge(componentEnv, PRIMITIVES); };
 
-  // String/number utilities for content addressing
-  PRIMITIVES["char-code-at"] = function(s, i) { return s.charCodeAt(i); };
-  PRIMITIVES["to-hex"] = function(n) { return (n >>> 0).toString(16); };
-
   // localStorage — defined here (before boot) so islands can use at hydration
   PRIMITIVES["local-storage-get"] = function(key) {
     try { var v = localStorage.getItem(key); return v === null ? NIL : v; }