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>

cart/sx/header.sx

@@ -7,38 +7,4 @@
   (a :href href :class "inline-flex items-center gap-1.5 px-3 py-1.5 text-sm rounded-full border border-stone-300 bg-white hover:bg-stone-50 transition"
     (i :class "fa fa-arrow-left text-xs" :aria-hidden "true") "All carts"))
 
-(defcomp ~cart-header-child (&key inner)
-  (div :id "root-header-child" :class "flex flex-col w-full items-center"
-    inner))
 
-(defcomp ~cart-header-child-nested (&key outer inner)
-  (div :id "root-header-child" :class "flex flex-col w-full items-center"
-    outer
-    (div :id "cart-header-child" :class "flex flex-col w-full items-center"
-      inner)))
-
-(defcomp ~cart-header-child-oob (&key inner)
-  (div :id "cart-header-child" :sx-swap-oob "outerHTML" :class "flex flex-col w-full items-center"
-    inner))
-
-(defcomp ~cart-auth-header-child (&key auth orders)
-  (div :id "root-header-child" :class "flex flex-col w-full items-center"
-    auth
-    (div :id "auth-header-child" :class "flex flex-col w-full items-center"
-      orders)))
-
-(defcomp ~cart-auth-header-child-oob (&key inner)
-  (div :id "auth-header-child" :sx-swap-oob "outerHTML" :class "flex flex-col w-full items-center"
-    inner))
-
-(defcomp ~cart-order-header-child (&key auth orders order)
-  (div :id "root-header-child" :class "flex flex-col w-full items-center"
-    auth
-    (div :id "auth-header-child" :class "flex flex-col w-full items-center"
-      orders
-      (div :id "orders-header-child" :class "flex flex-col w-full items-center"
-        order))))
-
-(defcomp ~cart-orders-header-child-oob (&key inner)
-  (div :id "orders-header-child" :sx-swap-oob "outerHTML" :class "flex flex-col w-full items-center"
-    inner))