fix: `ChessDisconnect`

[dadavidtseng]

[remote] ChessDisconnect [reason=""]: Send this command remotely to the connected computer, then disconnect yourself after sending. If the command includes a “remote=true” argument then it was sent to you from the remote host; disconnect your connection but do not re-send it back.
a. Example: “ChessDisconnect”
b. Example: “ChessDisconnect reason=Goodbye!”
c. Example: “ChessDisconnect reason="I have to go cook dinner."”

[dadavidtseng]

( DaemonChess ) fix: ChessDisconnect now is functional per assignment requirement

[dadavidtseng]

NOTE: NetworkSubsystem already handle disconnect scenario

[dadavidtseng]

( Engine ) feat: introduce GetValue(String const& keyName, unsigned short defaultValue) in NameStrings