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/content/highlight.py

@@ -236,14 +236,15 @@ def _tokenize_bash(code: str) -> list[tuple[str, str]]:
     return tokens
 
 
-def highlight(code: str, language: str = "lisp") -> str:
-    """Highlight code in the given language. Returns sx source."""
+def highlight(code: str, language: str = "lisp"):
+    """Highlight code in the given language. Returns SxExpr for wire format."""
+    from shared.sx.parser import SxExpr
     if language in ("lisp", "sx", "sexp"):
-        return highlight_sx(code)
+        return SxExpr(highlight_sx(code))
     elif language in ("python", "py"):
-        return highlight_python(code)
+        return SxExpr(highlight_python(code))
     elif language in ("bash", "sh", "shell"):
-        return highlight_bash(code)
+        return SxExpr(highlight_bash(code))
     # Fallback: no highlighting, just escaped text
     escaped = code.replace("\\", "\\\\").replace('"', '\\"')
-    return f'(span "{escaped}")'
+    return SxExpr(f'(span "{escaped}")')