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/navigation.sx

@@ -5,15 +5,22 @@
       (div :class "font-medium truncate" name)
       (div :class "text-xs text-stone-600 truncate" date-str))))
 
-(defcomp ~calendar-link-nav (&key href name nav-class)
-  (a :href href :class nav-class
+(defcomp ~calendar-link-nav (&key href name nav-class is-selected select-colours)
+  (a :href href
+     :sx-get href
+     :sx-target "#main-panel"
+     :sx-select "#main-panel"
+     :sx-swap "outerHTML"
+     :sx-push-url "true"
+     :aria-selected (when is-selected "true")
+     :class (str (or nav-class "") " " (or select-colours ""))
     (i :class "fa fa-calendar" :aria-hidden "true")
-    (div name)))
+    (span name)))
 
-(defcomp ~market-link-nav (&key href name nav-class)
-  (a :href href :class nav-class
+(defcomp ~market-link-nav (&key href name nav-class select-colours)
+  (a :href href :class (str (or nav-class "") " " (or select-colours ""))
     (i :class "fa fa-shopping-bag" :aria-hidden "true")
-    (div name)))
+    (span name)))
 
 (defcomp ~relation-nav (&key href name icon nav-class relation-type)
   (a :href href :class (or nav-class "flex items-center gap-3 rounded-lg py-2 px-3 text-sm text-stone-700 hover:bg-stone-100 transition-colors")