Fix station logout when deploying as a user

Running tofupilot deploy on a station required a user login, which previously overwrote the station's own credentials and stopped its service from starting.

• Fixed user and station logins so they no longer overwrite each other; a station stays authenticated after you log in as a user to deploy.
• Improved the station service so it keeps running after a user login on the same machine.
• Updated existing stations to migrate automatically on upgrade, with no re-login required.