fix(ui): send null (not '') for cleared organization_id on team update

AntD <Select allowClear> returns undefined when the user clears the
selection. Coalescing to "" caused the team-update payload to carry
organization_id: "" instead of null, relying on the backend to coerce
it. Send null directly so the intent is explicit at the source.

ui/litellm-dashboard/src/components/team/TeamInfo.tsx

@@ -495,7 +495,7 @@ const TeamInfoView: React.FC<TeamInfoProps> = ({
         },
         ...(values.policies?.length > 0 ? { policies: values.policies } : {}),
         ...(values.organization_id !== info.organization_id
-          ? { organization_id: values.organization_id ?? "" }
+          ? { organization_id: values.organization_id ?? null }
           : {}),
       };