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/App.tsx

@@ -28,8 +28,11 @@ function App() {
   
   // Listen for navigation events from main process
   useEffect(() => {
-    const handleNavigate = (path: string) => {
-      navigate(path);
+    const handleNavigate = (...args: unknown[]) => {
+      const path = args[0];
+      if (typeof path === 'string') {
+        navigate(path);
+      }
     };
     
     const unsubscribe = window.electron.ipcRenderer.on('navigate', handleNavigate);