Samba setup on labs: dual authenticated+guest access via setup-samba-auth.sh

Samba on RT-AX58U v2 (labs) runs unauthenticated (guest/share) by default. Windows blocks guest access by default → credentialed auth required for cross-platform. /home/byk/setup-samba-auth.sh enables both: sets Samba password for byk via smbpasswd -a byk (uid=1000, gid=1000, in groups adm/cdrom/sudo/dip/plugdev/lxd/docker). Windows access: \\100.69.65.125\Videos with creds byk + smbpasswd works on Windows/Android/Mac/iOS without client config. Guest path requires Windows registry tweak — credentials-only is the cross-platform recommendation. Chose credentialed auth over forcing Windows guest via registry because registry changes are per-client and brittle.