Janggi: highlight the general in bikjang

[Kadagaden]

When the generals are facing each other, highlight the player's general whose turn to move (like in check when red highlight is used).

It could be orange to differentiate it from check (red).

Example css:

background: #ffb60a;
filter: blur(10px);
border-radius: 10px;

[gbtami]

We should expose bikjang() https://github.com/ianfab/Fairy-Stockfish/blob/master/src/position.h#L176 in Fairy bindings to get this info.