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>

market/bp/fragments/routes.py

@@ -47,12 +47,14 @@ def register():
         if not markets:
             return ""
         styles = current_app.jinja_env.globals.get("styles", {})
-        nav_class = styles.get("nav_button_less_pad", "")
+        nav_class = styles.get("nav_button", "")
+        select_colours = current_app.jinja_env.globals.get("select_colours", "")
         parts = []
         for m in markets:
             href = market_url(f"/{post_slug}/{m.slug}/")
             parts.append(sx_call("market-link-nav",
-                                   href=href, name=m.name, nav_class=nav_class))
+                                   href=href, name=m.name, nav_class=nav_class,
+                                   select_colours=select_colours))
         return "(<> " + " ".join(parts) + ")"
 
     _handlers["container-nav"] = _container_nav_handler