feat(db): add database backup and initialization system

- Add backup.sh script for manual PostgreSQL database backups
- Update .gitignore to exclude pg_backups directory
- Modify docker-compose.yml to include backup service and volume mounts
- Add init.sh script for automated database initialization with backup restoration

backup.sh

@@ -0,0 +1,16 @@
+#!/bin/bash
+set -eu
+
+# Adjust these as needed:
+CONTAINER=worklenz_db
+DB_NAME=worklenz_db
+DB_USER=postgres
+BACKUP_DIR=./pg_backups
+mkdir -p "$BACKUP_DIR"
+
+timestamp=$(date +%Y-%m-%d_%H-%M-%S)
+outfile="${BACKUP_DIR}/${DB_NAME}_${timestamp}.sql"
+echo "Creating backup $outfile ..."
+
+docker exec -t "$CONTAINER" pg_dump -U "$DB_USER" -d "$DB_NAME" > "$outfile"
+echo "Backup saved to $outfile"