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>

shared/sx/templates/relations.sx

@@ -0,0 +1,15 @@
+(defcomp ~relation-attach (&key create-url label icon)
+  (a :href create-url
+     :sx-get create-url
+     :sx-target "#main-panel"
+     :sx-swap "outerHTML"
+     :sx-push-url "true"
+     :class "flex items-center gap-2 text-sm p-2 rounded hover:bg-stone-100 text-stone-500 hover:text-stone-700 transition-colors"
+    (when icon (i :class icon))
+    (span (or label "Add"))))
+
+(defcomp ~relation-detach (&key detach-url name)
+  (button :sx-delete detach-url
+          :sx-confirm (str "Remove " (or name "this item") "?")
+          :class "text-red-500 hover:text-red-700 text-sm p-1 rounded hover:bg-red-50 transition-colors"
+    (i :class "fa fa-times" :aria-hidden "true")))