Show sign-in window on first launch when user is not authenticated

**Summary**

When Coder Desktop is launched for the first time (or when the user is not signed in), the app should show the sign-in window instead of silently minimizing to the system tray. Currently, new users see no visible UI after launching the app, which makes it appear broken.

**Problem**

After a fresh install, launching Coder Desktop produces no visible window or taskbar entry. The app goes straight to the system tray as a background process. For a new user who has never used the app before:

1. There is no indication the app launched successfully
2. The user must discover the system tray icon (which Windows often hides behind the ^ overflow arrow)
3. The user must click the tray icon to find the sign-in prompt
4. The app cannot be used at all without signing in, so the silent tray behavior adds unnecessary friction

This leads users to believe the application failed to start — especially since Task Manager shows minimal CPU/memory activity, reinforcing the impression that nothing is happening.

**Proposed Behavior**

• First launch / not signed in: Show the sign-in window automatically. This gives the user a clear next step and confirms the app is running.
• Already authenticated: Continue the current behavior of going silently to the system tray.

Other system tray applications (such as Tailscale, 1Password) all show an onboarding or sign-in window on first launch before settling into tray-only mode.

El issue no menciona archivos, pruebas ni puntos de entrada. Empieza siguiendo la ruta de lanzamiento de la aplicación de Windows y cómo se comprueba el estado de autenticación; se considera terminado cuando un primer lanzamiento sin autenticación abre visiblemente la ventana de inicio de sesión, mientras que un lanzamiento autenticado continúa directamente en la bandeja del sistema.

Escrito por el modelo de indexación a partir del texto del issue.