Prepare Portainer stack deployment

.env.portainer.example

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+# Copy the needed values into Portainer under Stack > Environment variables.
+# Do not commit a filled production .env file.
+
+BACKEND_PORT=8112
+FRONTEND_PORT=8113
+LOG_LEVEL=info
+ALERT_DAYS_BEFORE=45
+SCHEDULER_INTERVAL_MINUTES=60
+APP_LOCALE=de
+AUTH_USERNAME=admin
+AUTH_PASSWORD=change-this-password
+AUTH_JWT_SECRET=change-this-to-a-long-random-secret
+AUTH_TOKEN_EXPIRES_IN_HOURS=12
+WATCHTOWER_ENABLE=false
+
+# Optional image names if Portainer should tag/pull custom images.
+# BACKEND_IMAGE=registry.example.com/paperless-contract-companion-api:latest
+# FRONTEND_IMAGE=registry.example.com/paperless-contract-companion-ui:latest
+
+# Optional public app URL for generated iCal/app links.
+# APP_EXTERNAL_URL=https://contracts.example.com
+
+# Optional paperless-ngx integration.
+# PAPERLESS_BASE_URL=http://paperless:8000
+# PAPERLESS_EXTERNAL_URL=https://paperless.example.com
+# PAPERLESS_TOKEN=replace-with-paperless-token
+
+# Optional ntfy push settings.
+# NTFY_SERVER_URL=https://ntfy.example.com
+# NTFY_TOPIC=contracts
+# NTFY_TOKEN=replace-with-ntfy-token
+# NTFY_PRIORITY=high
+
+# Optional mail settings.
+# MAIL_SERVER=smtp.example.com
+# MAIL_PORT=587
+# MAIL_USERNAME=mailer
+# MAIL_PASSWORD=replace-with-mail-password
+# MAIL_USE_TLS=true
+# MAIL_FROM=contract-monitor@example.com
+# MAIL_TO=you@example.com
+
+# Optional fixed iCal token.
+# ICAL_SECRET=replace-with-long-random-token