Rebrand sexp → sx across web platform (173 files)

Rename all sexp directories, files, identifiers, and references to sx.
artdag/ excluded (separate media processing DSL).

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

orders/bp/fragments/routes.py

@@ -14,9 +14,9 @@ def register():
 
     async def _account_nav_item():
         from shared.infrastructure.urls import orders_url
-        from shared.sexp.helpers import sexp_call
+        from shared.sx.helpers import sx_call
 
-        return sexp_call("account-nav-item",
+        return sx_call("account-nav-item",
                          href=orders_url("/"),
                          label="orders")
 
@@ -33,8 +33,8 @@ def register():
     async def get_fragment(fragment_type: str):
         handler = _handlers.get(fragment_type)
         if handler is None:
-            return Response("", status=200, content_type="text/sexp")
+            return Response("", status=200, content_type="text/sx")
         src = await handler()
-        return Response(src, status=200, content_type="text/sexp")
+        return Response(src, status=200, content_type="text/sx")
 
     return bp