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/en.ts

@@ -219,6 +219,11 @@ export default {
   'offline.message': 'You are currently offline. Some features may be limited.',
   'syncing.title': 'Syncing…',
   'syncing.message': 'Your data is being synchronized.',
+  'reconnecting.message': 'Reconnecting...',
+
+  // Send blocked
+  'send.blocked.title': 'Cannot send message',
+  'send.blocked.noConnection': 'Not connected to server',
 
   // Install prompt
   'install.title': 'Install HAPI',