fix(normalizer): handle None return from _parse_wfigs_incidents

When the non-WF filter returns None, the caller must check before
assigning to n[_kind]. Fixes TypeError on non-wildfire incidents.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

meshai/central_normalizer.py

@@ -826,6 +826,8 @@ def normalize(envelope: dict) -> Optional[dict]:
             }
         if category_raw.startswith("fire.incident"):
             n = _parse_wfigs_incidents(inner_data, geo)
+            if n is None:
+                return None
             n["_kind"] = "wfigs_incident"
             return n
     if adapter == "wfigs_perimeters":