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/social.sx

@@ -6,9 +6,6 @@
   (nav :class "flex gap-3 text-sm items-center"
     (a :href url :class "px-2 py-1 rounded hover:bg-stone-200 font-bold" "Choose username")))
 
-(defcomp ~federation-nav-link (&key href cls label)
-  (a :href href :class cls label))
-
 (defcomp ~federation-nav-notification-link (&key href cls count-url)
   (a :href href :class cls "Notifications"
     (span :sx-get count-url :sx-trigger "load, every 30s" :sx-swap "innerHTML"
@@ -21,35 +18,29 @@
   (div :id "social-row" :class "flex flex-col items-center md:flex-row justify-center md:justify-between w-full p-1 bg-sky-400"
     (div :class "w-full flex flex-row items-center gap-2 flex-wrap" nav)))
 
-(defcomp ~federation-header-child (&key inner)
-  (div :id "root-header-child" :class "flex flex-col w-full items-center" inner))
-
 ;; --- Post card ---
 
 (defcomp ~federation-boost-label (&key name)
   (div :class "text-sm text-stone-500 mb-2" "Boosted by " name))
 
+;; Aliases — delegate to shared ~avatar
 (defcomp ~federation-avatar-img (&key src cls)
-  (img :src src :alt "" :class cls))
+  (~avatar :src src :cls cls))
 
 (defcomp ~federation-avatar-placeholder (&key cls initial)
-  (div :class cls initial))
+  (~avatar :cls cls :initial initial))
 
-(defcomp ~federation-content-cw (&key summary content)
-  (details :class "mt-2"
-    (summary :class "text-stone-500 cursor-pointer" "CW: " (~rich-text :html summary))
+(defcomp ~federation-content (&key content summary)
+  (if summary
+    (details :class "mt-2"
+      (summary :class "text-stone-500 cursor-pointer" "CW: " (~rich-text :html summary))
+      (div :class "mt-2 prose prose-sm prose-stone max-w-none" (~rich-text :html content)))
     (div :class "mt-2 prose prose-sm prose-stone max-w-none" (~rich-text :html content))))
 
-(defcomp ~federation-content-plain (&key content)
-  (div :class "mt-2 prose prose-sm prose-stone max-w-none" (~rich-text :html content)))
-
 (defcomp ~federation-original-link (&key url)
   (a :href url :target "_blank" :rel "noopener"
     :class "text-sm text-stone-400 hover:underline mt-1 inline-block" "original"))
 
-(defcomp ~federation-interactions-wrap (&key id buttons)
-  (div :id id buttons))
-
 (defcomp ~federation-post-card (&key boost avatar actor-name actor-username domain time content original interactions)
   (article :class "bg-white rounded-lg shadow-sm border border-stone-200 p-4 mb-4"
     boost