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/browser/app/errors.py

@@ -223,16 +223,21 @@ def errors(app):
                 errnum='403'
             )
         else:
-            try:
-                html = _sx_error_page(
-                    "403", "FORBIDDEN",
-                    image="/static/errors/403.gif",
-                )
-            except Exception:
-                html = await render_template(
-                    "_types/root/exceptions/_.html",
-                    errnum='403',
-                )
+            html = await _rich_error_page(
+                "403", "FORBIDDEN",
+                image="/static/errors/403.gif",
+            )
+            if html is None:
+                try:
+                    html = _sx_error_page(
+                        "403", "FORBIDDEN",
+                        image="/static/errors/403.gif",
+                    )
+                except Exception:
+                    html = await render_template(
+                        "_types/root/exceptions/_.html",
+                        errnum='403',
+                    )
 
         return await make_response(html, 403)
 
@@ -291,7 +296,11 @@ def errors(app):
                 status,
             )
 
-        # Raw HTML — avoids context processor / fragment loop on errors.
-        return await make_response(_error_page(
-            "WELL THIS IS EMBARRASSING…"
-        ), status)
+        errnum = str(status)
+        html = await _rich_error_page(
+            errnum, "WELL THIS IS EMBARRASSING\u2026",
+            image="/static/errors/error.gif",
+        )
+        if html is None:
+            html = _error_page("WELL THIS IS EMBARRASSING…")
+        return await make_response(html, status)