add Yani's fellowship (#1331)

Author: maelle

data/team/team.json

@@ -89,7 +89,8 @@
     "url": "/author/yanina-bellini-saibene/",
     "image": "/img/team/yanina-bellini-saibene.jpg",
     "roles": [
-      "staff"
+      "staff",
+      "2026 Sovereign Tech Fellow"
     ],
     "leads": [
       "champions",