feat: add !artist command for artist-based loop playback

src/bot/commands.ts

@@ -8,6 +8,7 @@ export interface ParsedCommand {
 export const PUBLIC_COMMANDS = new Set([
   "play", "add", "queue", "list", "now", "lyrics", "vote", "help",
   "playlist", "album", "fm", "prev", "next", "skip", "pause", "resume",
+  "artist",
 ]);
 
 export const ADMIN_COMMANDS = new Set([