Default to the configured public org on initial load

### Is your feature request related to a problem?

When accessing the private-mirrors UI, users are presented with a page where they can select the desired organization to create a mirror in after logging in. This landing page adds an additional click for the user that is unnecessary.

### Describe the solution you'd like

To remove the need to select an organization, private-mirrors should default to the configured public org and automatically navigate to its page when the user logs in.

### Describe alternatives you've considered

The current landing page may be desirable if private-mirrors is updated to support syncing between multiple orgs but the app can be updated to handle cases where there are multiple public orgs specified in the future when that feature is supported.

### Additional context

_No response_