feat: add user reset-apikey command

Adds `hf user reset-apikey <username>` to regenerate a user API key.
Requires user.manage permission. Returns the new key (shown once only).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

cmd/hf/main.go

@@ -341,6 +341,11 @@ func handleUserCommand(subCmd string, args []string) {
 			output.Error("usage: hf user delete <username>")
 		}
 		commands.RunUserDelete(filtered[0], tokenFlag)
+	case "reset-apikey":
+		if len(filtered) < 1 {
+			output.Error("usage: hf user reset-apikey <username>")
+		}
+		commands.RunUserResetAPIKey(filtered[0], tokenFlag)
 	default:
 		output.Errorf("hf user %s is not implemented yet", subCmd)
 	}