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>

account/bp/fragments/routes.py

@@ -1,6 +1,6 @@
 """Account app fragment endpoints.
 
-Exposes sexp fragments at ``/internal/fragments/<type>`` for consumption
+Exposes sx fragments at ``/internal/fragments/<type>`` for consumption
 by other coop apps via the fragment client.
 
 Fragments:
@@ -18,15 +18,15 @@ def register():
     bp = Blueprint("fragments", __name__, url_prefix="/internal/fragments")
 
     # ---------------------------------------------------------------
-    # Fragment handlers — return sexp source text
+    # Fragment handlers — return sx source text
     # ---------------------------------------------------------------
 
     async def _auth_menu():
         from shared.infrastructure.urls import account_url
-        from shared.sexp.helpers import sexp_call
+        from shared.sx.helpers import sx_call
 
         user_email = request.args.get("email", "")
-        return sexp_call("auth-menu",
+        return sx_call("auth-menu",
                          user_email=user_email or None,
                          account_url=account_url(""))
 
@@ -47,8 +47,8 @@ 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