Electerm WebSocket `upgrade-func` and `fs` handlers allow arbitrary method/function invocation due to missing method-name allowlist

electerm is an open-sourced terminal/ssh/sftp/telnet/serialport/RDP/VNC/Spice/ftp client. Prior to 3.15.186, electerm allows an authenticated WebSocket client to invoke unintended internal functions through client-controlled func values in upgrade-func in src/app/server/dispatch-center.js and handleFs in src/app/server/fs.js, exposing Upgrade and fsExport methods that can execute commands, open files, mutate the filesystem, or terminate the process. This issue is fixed in version 3.15.186.