Replace the App-identity !gh text command with native slash and message
context-menu commands. /gh login|logout link a Discord user to their GitHub
account; /gh comment add|edit|del and the right-click 'GitHub' commands open
a modal and create/edit/delete comments using the user's own OAuth token,
delegating permission checks to GitHub (surfacing 401/403/404). The gateway
registers guild commands on connect and handles interactions in the DO.
