CRITICAL FIX: Prevent Electron from quitting in SignalR mode

ROOT CAUSE: Electron quits when app.on('ready') completes with 0 windows.
In SignalR mode, no windows are created immediately, so Electron exits,
triggering ElectronProcess_Stopped and shutting down ASP.NET.

SOLUTION: Create an invisible 1x1 keep-alive window in SignalR mode to
prevent Electron from quitting while waiting for SignalR connection.

Also:
- Make app.on('ready') async and await startSignalRApiBridge()
- Add window-all-closed handler for SignalR mode
- Add extensive debug logging to track lifecycle
- Don't subscribe to electronProcess.Ready in SignalR controller

This fixes the premature shutdown that prevented SignalR connection.

src/ElectronNET.Samples.BlazorSignalR/appsettings.Development.json

@@ -2,7 +2,9 @@
   "Logging": {
     "LogLevel": {
       "Default": "Information",
-      "Microsoft.AspNetCore": "Warning"
+      "Microsoft.AspNetCore": "Warning",
+      "Microsoft.AspNetCore.SignalR": "Debug",
+      "Microsoft.AspNetCore.Http.Connections": "Debug"
     }
   }
 }