White-label preview: brings up cms + cms-db + mail + pdf + nginx +
shop with placeholder env so the toolkit runs clickably without
any adapter. Adapters (e.g. mp) replace compose.yaml with their own
composition + branding env.
Every libreshop component image is pinned to :v0.1.0 — override per
service via LIBRESHOP_<SVC>_TAG in .env if testing rolling :main.
.env.example documents every variable; mail stays in stdout-log
mode and PayPal stays in sandbox/no-creds mode by default.
