Parse or save the UserAgent of login requests to have a meaningful session name

[CrescentKohana]

Either

• Save the raw user agent as the session name and let client handle the parsing
  • OR
• Parse the UserAgent and save the result

https://github.com/Mangatsu/server/blob/d5e49ae09508adf12ee31939a6d642b238e64da7/pkg/api/user.go#L74

[CrescentKohana]

This is a frontend issue as next-auth always sends node-fetch/1.0 (+https://github.com/bitinn/node-fetch) as the user agent.

Made the name a bit user-friendlier here https://github.com/Mangatsu/web/commit/1589f6a913a5aade35b3baf8b94cfb6d9d2c1470