fix: offlineBanner uses getIntl() and inline network state

OfflineBanner is rendered inside rootContainer, which is the outermost
wrapper in Umi's provider chain. useModel('network') and useIntl()
require provider context (dataflowProvider, i18nProvider) that doesn't
exist at this level, causing runtime crashes. Switch to getIntl() (which
accesses the global intl singleton) and inline navigator.onLine state.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/components/OfflineBanner/index.tsx

@@ -1,9 +1,22 @@
-import { useIntl, useModel } from '@umijs/max';
+import { getIntl } from '@umijs/max';
 import { Alert } from 'antd';
+import { useEffect, useState } from 'react';
 
 const OfflineBanner: React.FC = () => {
-  const { isOnline } = useModel('network');
-  const intl = useIntl();
+  const [isOnline, setIsOnline] = useState(
+    typeof navigator !== 'undefined' ? navigator.onLine : true,
+  );
+
+  useEffect(() => {
+    const handleOnline = () => setIsOnline(true);
+    const handleOffline = () => setIsOnline(false);
+    window.addEventListener('online', handleOnline);
+    window.addEventListener('offline', handleOffline);
+    return () => {
+      window.removeEventListener('online', handleOnline);
+      window.removeEventListener('offline', handleOffline);
+    };
+  }, []);
 
   if (isOnline) return null;
 
@@ -12,7 +25,7 @@ const OfflineBanner: React.FC = () => {
       type="warning"
       banner
       closable={false}
-      message={intl.formatMessage({ id: 'app.network.offline' })}
+      message={getIntl().formatMessage({ id: 'app.network.offline' })}
     />
   );
 };