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>

shared/sx/templates/layout.sx

@@ -68,7 +68,9 @@
         (when cart-mini cart-mini)
         (div :class "font-bold text-5xl flex-1"
           (a :href (or blog-url "/") :class "flex justify-center md:justify-start items-baseline gap-2"
-            (h1 (or site-title ""))))
+            (h1 (or site-title ""))
+            (when app-label
+              (span :class "text-lg text-white/80 font-normal" app-label))))
         (nav :class "hidden md:flex gap-4 text-sm ml-2 justify-end items-center flex-0"
           (when nav-tree nav-tree)
           (when auth-menu auth-menu)