feat(06-02): add environment docs and backup script

- .env.example documents all configuration options
- backup.sh creates timestamped archive of Docker volume
- Supports custom volume name via VOLUME_NAME env var

backup.sh

@@ -0,0 +1,47 @@
+#!/bin/bash
+# TaskPlaner Data Backup Script
+# Creates a timestamped backup of the Docker volume
+
+set -e
+
+# Configuration (override via environment)
+BACKUP_DIR="${BACKUP_DIR:-./backups}"
+VOLUME_NAME="${VOLUME_NAME:-taskplaner_taskplaner_data}"
+TIMESTAMP=$(date +%Y%m%d_%H%M%S)
+BACKUP_FILE="${BACKUP_DIR}/taskplaner_backup_${TIMESTAMP}.tar.gz"
+
+# Create backup directory if needed
+mkdir -p "$BACKUP_DIR"
+
+echo "========================================="
+echo "TaskPlaner Backup"
+echo "========================================="
+echo "Volume: $VOLUME_NAME"
+echo "Output: $BACKUP_FILE"
+echo ""
+
+# Check if volume exists
+if ! docker volume inspect "$VOLUME_NAME" > /dev/null 2>&1; then
+  echo "Error: Volume '$VOLUME_NAME' not found"
+  echo ""
+  echo "Available volumes:"
+  docker volume ls --format '  - {{.Name}}' | grep -i taskplaner || echo "  (none with 'taskplaner' in name)"
+  echo ""
+  echo "Tip: Set VOLUME_NAME environment variable to use a different volume"
+  exit 1
+fi
+
+# Create backup using temporary Alpine container
+echo "Creating backup..."
+docker run --rm \
+  -v "${VOLUME_NAME}:/data:ro" \
+  -v "$(cd "$BACKUP_DIR" && pwd):/backup" \
+  alpine:latest \
+  tar czf "/backup/taskplaner_backup_${TIMESTAMP}.tar.gz" -C /data .
+
+echo ""
+echo "Backup complete!"
+echo "File: $BACKUP_FILE"
+echo "Size: $(du -h "$BACKUP_FILE" | cut -f1)"
+echo ""
+echo "To restore: docker run --rm -v ${VOLUME_NAME}:/data -v \$(pwd)/${BACKUP_DIR}:/backup alpine tar xzf /backup/taskplaner_backup_${TIMESTAMP}.tar.gz -C /data"