feat(web): Add reconnecting feedback when SSE connection is lost (#125)

- Add ReconnectingBanner component to show "Reconnecting..." status
- Track SSE connection state in App.tsx with onDisconnect handler
- Add onBlocked callback to useSendMessage for handling blocked send attempts
- Provide haptic feedback when send is blocked due to no API or session
- Show toast notification when message cannot be sent due to server disconnection
- Add translation keys for reconnecting message and send blocked feedback in en/zh-CN

close #125

web/src/lib/locales/zh-CN.ts

@@ -221,6 +221,11 @@ export default {
   'offline.message': '您当前处于离线状态。某些功能可能受限。',
   'syncing.title': '同步中…',
   'syncing.message': '正在同步您的数据。',
+  'reconnecting.message': '正在重新连接...',
+
+  // Send blocked
+  'send.blocked.title': '无法发送消息',
+  'send.blocked.noConnection': '未连接到服务器',
 
   // Install prompt
   'install.title': '安装 HAPI',