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>

federation/sx/search.sx

@@ -1,10 +1,11 @@
 ;; Search and actor card components
 
+;; Aliases — delegate to shared ~avatar
 (defcomp ~federation-actor-avatar-img (&key src cls)
-  (img :src src :alt "" :class cls))
+  (~avatar :src src :cls cls))
 
 (defcomp ~federation-actor-avatar-placeholder (&key cls initial)
-  (div :class cls initial))
+  (~avatar :cls cls :initial initial))
 
 (defcomp ~federation-actor-name-link (&key href name)
   (a :href href :class "font-semibold text-stone-900 hover:underline" name))