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>

market/sx/grids.sx

@@ -3,17 +3,9 @@
 (defcomp ~market-markets-grid (&key cards)
   (div :class "max-w-full px-3 py-3 grid grid-cols-1 sm:grid-cols-2 md:grid-cols-3 gap-4" cards))
 
-(defcomp ~market-no-markets (&key message)
-  (div :class "px-3 py-12 text-center text-stone-400"
-    (i :class "fa fa-store text-4xl mb-3" :aria-hidden "true")
-    (p :class "text-lg" message)))
-
 (defcomp ~market-product-grid (&key cards)
   (<> (div :class "grid grid-cols-1 sm:grid-cols-3 md:grid-cols-6 gap-3" cards) (div :class "pb-8")))
 
-(defcomp ~market-bottom-spacer ()
-  (div :class "pb-8"))
-
 (defcomp ~market-like-toggle-button (&key colour action hx-headers label icon-cls)
   (button :class (str "flex items-center gap-1 " colour " hover:text-red-600 transition-colors w-[1em] h-[1em]")
           :sx-post action :sx-target "this" :sx-swap "outerHTML" :sx-push-url "false"