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/stores/cron.ts

@@ -20,7 +20,7 @@ interface CronState {
   setJobs: (jobs: CronJob[]) => void;
 }
 
-export const useCronStore = create<CronState>((set, get) => ({
+export const useCronStore = create<CronState>((set) => ({
   jobs: [],
   loading: false,
   error: null,