feat(backup): 3-2-1 backup strategy with multi-target support

.env.example

@@ -106,6 +106,38 @@ OLLAMA_GPU_ENABLED=false       # Set to true if you have NVIDIA GPU
 GOTIFY_PASSWORD=               # REQUIRED
 NTFY_AUTH_ENABLED=true
 
+# -----------------------------------------------------------------------------
+# BACKUP CONFIGURATION (3-2-1 Strategy)
+# -----------------------------------------------------------------------------
+# Backup destination: local | s3 | b2 | sftp | r2
+BACKUP_TARGET=local
+BACKUP_DIR=/opt/homelab-backups
+RETENTION_DAYS=7
+
+# ntfy notifications for backup status
+NTFY_HOST=http://ntfy
+NTFY_TOPIC=homelab-backup
+
+# S3 / MinIO / R2 (BACKUP_TARGET=s3 or r2)
+AWS_ACCESS_KEY_ID=
+AWS_SECRET_ACCESS_KEY=
+AWS_ENDPOINT=                  # Omit for AWS S3. Use R2 endpoint for Cloudflare R2.
+AWS_BUCKET=homelab-backups
+AWS_REGION=us-east-1           # Use "auto" for Cloudflare R2
+
+# Backblaze B2 (BACKUP_TARGET=b2)
+B2_ACCOUNT_ID=
+B2_ACCOUNT_KEY=
+B2_BUCKET=homelab-backups
+
+# SFTP (BACKUP_TARGET=sftp)
+SFTP_HOST=
+SFTP_PORT=22
+SFTP_USER=
+SFTP_PASSWORD=
+SFTP_KEY=                      # Path to SSH private key (alternative to password)
+SFTP_REMOTE_DIR=/backups
+
 # -----------------------------------------------------------------------------
 # NETWORK PROXY (optional — for CN users with local proxy)
 # -----------------------------------------------------------------------------