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>

blog/sx/detail.sx

@@ -52,9 +52,3 @@
 
 (defcomp ~blog-home-main (&key html-content)
   (article :class "relative" (div :class "blog-content p-2" (~rich-text :html html-content))))
-
-(defcomp ~blog-admin-empty ()
-  (div :class "pb-8"))
-
-(defcomp ~blog-settings-empty ()
-  (div :class "max-w-2xl mx-auto px-4 py-6"))