docs(infra): add .env.example with OCR_TRAINING_TOKEN

Fresh cloners had no tracked reference for required env vars.
.env is gitignored (contains real credentials). .env.example
documents all variables including the new OCR_TRAINING_TOKEN
for the Python OCR microservice training endpoints.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.env.example

@@ -0,0 +1,36 @@
+# Datenbank (PostgreSQL)
+POSTGRES_USER=archive_user
+POSTGRES_PASSWORD=change-me
+POSTGRES_DB=family_archive_db
+
+# Object Storage (MinIO)
+MINIO_ROOT_USER=minio_admin
+MINIO_ROOT_PASSWORD=change-me
+MINIO_DEFAULT_BUCKETS=archive-documents
+
+# Ports (für Zugriff vom Host/NAS)
+PORT_DB=5432
+PORT_MINIO_API=9000
+PORT_MINIO_CONSOLE=9001
+PORT_BACKEND=8080
+PORT_FRONTEND=5173
+
+# Mailpit — local mail catcher (dev only, included in docker-compose)
+# Web UI:  http://localhost:8025
+# SMTP:    localhost:1025  (used automatically by the backend container)
+PORT_MAILPIT_UI=8100
+PORT_MAILPIT_SMTP=1025
+
+# OCR Training — set a secret token to protect the /train and /segtrain endpoints on the
+# Python OCR microservice. Leave empty to disable token authentication (development only).
+# OCR_TRAINING_TOKEN=change-me-in-production
+
+# Production SMTP — uncomment and fill in to send real emails instead of catching them
+# APP_BASE_URL=https://your-domain.example.com
+# MAIL_HOST=smtp.example.com
+# MAIL_PORT=587
+# MAIL_USERNAME=your-smtp-user
+# MAIL_PASSWORD=your-smtp-password
+# MAIL_SMTP_AUTH=true
+# MAIL_STARTTLS_ENABLE=true
+# APP_MAIL_FROM=noreply@your-domain.example.com