Own pinned alpine image (3.21@sha256:48b0309c) + smbd/nmbd/wsdd/tini. Dumb by
design: smb.conf bind-mounted read-only, no baked name/password, passdb on a
volume. Three-daemon stack per the R-6 spike verdict (nmbd required alongside
wsdd, else Explorer double-click 0x80070035). build-samba-image.sh helper.
