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>

shared/sx/helpers.py

@@ -627,8 +627,9 @@ def sx_page(ctx: dict, page_sx: str, *,
     component_hash = get_component_hash()
 
     # Check if client already has this version cached (via cookie)
+    # In dev mode, always send full source so edits are visible immediately
     client_hash = _get_sx_comp_cookie()
-    if client_hash and client_hash == component_hash:
+    if not _is_dev_mode() and client_hash and client_hash == component_hash:
         # Client has current components cached — send empty source
         component_defs = ""
     else:
@@ -675,7 +676,7 @@ def sx_page(ctx: dict, page_sx: str, *,
     # Style dictionary for client-side css primitive
     styles_hash = _get_style_dict_hash()
     client_styles_hash = _get_sx_styles_cookie()
-    if client_styles_hash and client_styles_hash == styles_hash:
+    if not _is_dev_mode() and client_styles_hash and client_styles_hash == styles_hash:
         styles_json = ""  # Client has cached version
     else:
         styles_json = _build_style_dict_json()