fix(usage): ensure refresh button shows loading animation on click

Changed from isLoading to isFetching to properly track all query states.
Previously, the refresh button spinner would not animate when clicking
refresh because isLoading only indicates initial load without cached data.
isFetching covers all query states including manual refetches.

src/components/UsageFooter.tsx

@@ -19,7 +19,7 @@ const UsageFooter: React.FC<UsageFooterProps> = ({
   const { t } = useTranslation();
   const {
     data: usage,
-    isLoading: loading,
+    isFetching: loading,
     refetch,
   } = useUsageQuery(providerId, appId, usageEnabled);