feat(gateway): enhance gateway process management with auto-reconnection

Improve Gateway lifecycle management with the following features:

- Add exponential backoff reconnection (1s-30s delay, max 10 attempts)
- Add health check monitoring every 30 seconds
- Add proper restart method with graceful shutdown
- Handle server-initiated notifications (channel status, chat messages)
- Add 'reconnecting' state for better UI feedback
- Enhance IPC handlers with isConnected and health check endpoints
- Update preload script with new event channels
- Improve type safety and error handling throughout

Also fixes several TypeScript errors and unused variable warnings.

src/pages/Cron/index.tsx

@@ -2,7 +2,7 @@
  * Cron Page
  * Manage scheduled tasks
  */
-import { useEffect, useState } from 'react';
+import { useEffect } from 'react';
 import { Plus, Clock, Play, Pause, Trash2, Edit, RefreshCw } from 'lucide-react';
 import { Button } from '@/components/ui/button';
 import { Card, CardContent, CardDescription, CardHeader, CardTitle } from '@/components/ui/card';