Refactor SX templates: shared components, Python migration, cleanup

- Extract shared components (empty-state, delete-btn, sentinel, crud-*,
  view-toggle, img-or-placeholder, avatar, sumup-settings-form, auth
  forms, order tables/detail/checkout)
- Migrate all Python sx_call() callers to use shared components directly
- Remove 55+ thin wrapper defcomps from domain .sx files
- Remove trivial passthrough wrappers (blog-header-label, market-card-text, etc)
- Unify duplicate auth flows (account + federation) into shared/sx/templates/auth.sx
- Unify duplicate order views (cart + orders) into shared/sx/templates/orders.sx
- Disable static file caching in dev (SEND_FILE_MAX_AGE_DEFAULT=0)
- Add SX response validation and debug headers

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

events/sx/forms.sx

@@ -494,8 +494,4 @@
 
 (defcomp ~events-admin-placeholder-nav ()
   (div :class "relative nav-group"
-    (span :class "block px-3 py-2 text-stone-400 text-sm italic" "Admin options")))
-
-;; Entry admin main panel — ticket_types link
-(defcomp ~events-entry-admin-main-panel (&key link)
-  link)
+    (span :class "block px-3 py-2 text-stone-400 text-sm italic" "Admin options")))