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.
