User should be able to resign a game (= become defeated on its own)

[CrsiX]

At the moment, it looks like neither the server nor the client checks if a player is still participating. We either need a new API endpoint for that or let the server inspect the uploaded game file.

What exactly happens at the moment?

[CrsiX]

If any of the players is defeated, they will still receive game updates, but won't be able to perform any moves and are not required to perform turns, i.e. the game will silently continue properly without any actions of them.

[CrsiX]

When somebody wins a game, it will currently remain on the server, so everybody else can still join the game. The winner will see the victory screen, but could also continue playing in single-player manner. However, the single-player experience is somewhat cumbersome at the moment, since the auto-detection that it's the current user's turn doesn't work (yet).

[CrsiX]

Winning is no problem after the patch I posted upstream.
Resigning is not implemented in the UI. This should be addressed in this issue.