feat: standalone libreshop demo stack pinned to v0.1.0

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.

.env.example

@@ -0,0 +1,42 @@
+# libreshop/demo — copy to .env and edit. Defaults below are
+# placeholder values; the stack boots clickably with them but mail
+# stays in stdout-log mode and PayPal stays in sandbox/no-creds mode.
+
+# Pinned versions (override per service if you want to test :main).
+LIBRESHOP_CMS_TAG=v0.1.0
+LIBRESHOP_MAIL_TAG=v0.1.0
+LIBRESHOP_PDF_TAG=v0.1.0
+LIBRESHOP_SHOP_TAG=v0.1.0
+LIBRESHOP_NGINX_TAG=v0.1.0
+
+# Where the demo binds nginx (host port).
+LIBRESHOP_DEMO_PORT=8080
+
+# Strapi DB (local-only credentials; rotate for any non-toy run).
+CMS_DB_NAME=libreshop
+CMS_DB_USER=libreshop
+CMS_DB_PASSWORD=changeme-in-prod
+
+# Strapi secrets — generate real values with: openssl rand -base64 32
+CMS_JWT_SECRET=changeme-jwt-secret-32-bytes-min!!!
+CMS_API_TOKEN_SALT=changeme-api-token-salt
+CMS_ADMIN_JWT_SECRET=changeme-admin-jwt-secret
+CMS_APP_KEYS=key-a,key-b,key-c,key-d
+CMS_TRANSFER_TOKEN_SALT=changeme-transfer-salt
+ADMIN_EMAIL_ADDRESS=admin@example.invalid
+
+# Mail relay — leave blank for stdout-log mode (no real email sent).
+MAIL_SMTP_RELAY_HOST=
+MAIL_SMTP_RELAY_PORT=587
+MAIL_SMTP_RELAY_USERNAME=
+MAIL_SMTP_RELAY_PASSWORD=
+
+# Shop runtime — placeholder demo token, no PayPal client.
+SHOP_API_TOKEN=demo-shop-api-token
+SHOP_SITE_URL=http://localhost:8080
+SHOP_BASE_URL=/
+PAYMENT_ENVIRONMENT=sandbox
+PAYPAL_CLIENT_ID=
+
+# Nginx host header (browser sees this; localhost is fine for the demo).
+NGINX_HOST=localhost