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>

federation/bp/fragments/routes.py

@@ -1,6 +1,6 @@
 """Federation 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.
 """
 
@@ -25,15 +25,15 @@ 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")
 
     # --- link-card fragment: actor profile preview card --------------------------
 
-    def _federation_link_card_sexp(actor, link: str) -> str:
-        from shared.sexp.helpers import sexp_call
-        return sexp_call("link-card",
+    def _federation_link_card_sx(actor, link: str) -> str:
+        from shared.sx.helpers import sx_call
+        return sx_call("link-card",
                          link=link,
                          title=actor.display_name or actor.preferred_username,
                          image=None,
@@ -59,7 +59,7 @@ def register():
                 parts.append(f"<!-- fragment:{u} -->")
                 actor = await services.federation.get_actor_by_username(g.s, u)
                 if actor:
-                    parts.append(_federation_link_card_sexp(
+                    parts.append(_federation_link_card_sx(
                         actor, federation_url(f"/users/{actor.preferred_username}"),
                     ))
             return "\n".join(parts)
@@ -71,7 +71,7 @@ def register():
         actor = await services.federation.get_actor_by_username(g.s, lookup)
         if not actor:
             return ""
-        return _federation_link_card_sexp(
+        return _federation_link_card_sx(
             actor, federation_url(f"/users/{actor.preferred_username}"),
         )