Fix _aser_call and sx_call list serialization: use (list ...) for data arrays

Data lists (dicts, strings, numbers) were wrapped in (<> ...) fragments
which the client rendered as empty DocumentFragments instead of iterable
arrays. This broke map/filter over cards, tag_groups, and authors in
blog index and similar components.

- _aser_call: data lists → (list ...), rendered content (SxExpr) → (<> ...)
- sx_call: all list kwargs → (list ...)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

shared/sx/helpers.py

@@ -404,13 +404,22 @@ def sx_call(component_name: str, **kwargs: Any) -> str:
 
     Values are serialized: strings are quoted, None becomes nil,
     bools become true/false, numbers stay as-is.
+    List values use ``(list ...)`` so the client gets an iterable array
+    rather than a rendered fragment.
     """
-    from .parser import serialize
+    from .parser import serialize, SxExpr
     name = component_name if component_name.startswith("~") else f"~{component_name}"
     parts = [name]
     for key, val in kwargs.items():
         parts.append(f":{key.replace('_', '-')}")
-        parts.append(serialize(val))
+        if isinstance(val, list):
+            items = [serialize(v) for v in val if v is not None]
+            if not items:
+                parts.append("nil")
+            else:
+                parts.append("(list " + " ".join(items) + ")")
+        else:
+            parts.append(serialize(val))
     return "(" + " ".join(parts) + ")"