refactor(docker-monolithic): refactor backup script to use docker cp

[bytestream]

Rather than copying to tmp directory within the container, we can simplify the process and just copy directly to the host.

[Copilot]

Pull Request Overview

This PR refactors the Docker monolithic backup script to use docker cp for copying files directly from the container to the host, eliminating the intermediate step of copying files to a temporary directory within the container first.

Key Changes:

• Replaced container-based file operations (docker compose exec ... cp) with docker cp commands that copy directly to the host
• Changed TEMP_BACKUP_DIR (container path /tmp/tmp-backups/${TIMESTAMP}) to TMP_DIR (host path ${ABS_BACKUP_PATH}/tmp-${TIMESTAMP})
• Simplified cleanup by only needing to remove the host temporary directory instead of both host and container cleanup

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[Copilot]

[nitpick] The comment mentions "container cleanup is minimal" but there's no longer any container cleanup happening in this refactored version. The database backup file is explicitly deleted from the container on line 86, which is the only cleanup. Consider updating the comment to be more accurate, e.g., "Cleanup temporary directory from host" or "Cleanup (database backup already removed from container on line 86)".

Suggested change

	# Cleanup (now only needs to clean the host TMP_DIR, container cleanup is minimal)
	# Cleanup temporary directory from host (database backup already removed from container on line 86)