Add pfSense backup utility and documentation

- Add backup-pfsense-config.sh script for automated config backups via SSH
- Auto-commits backups to git with timestamped filenames
- Includes validation, error handling, and troubleshooting guides
- Add scripts/README.md with detailed usage and crontab examples
- Add BACKUP-QUICKSTART.md for quick reference commands
- Update README.md to reference automated backup workflow
- Create backups/ directory structure

The script tests SSH connectivity successfully to pfSense.

pfsense.home.arpa/backups/.gitkeep

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+# Backups Directory
+
+pfSense configuration backups are stored here with timestamped filenames.
+
+**DO NOT delete backup files without understanding the implications.**
+
+Format: `pfsense-config-YYYY-MM-DD_HHMMSS.xml`
+
+All backup files are committed to git, so previous versions can be restored from git history if needed.
+
+For backup automation, see: [scripts/README.md](../scripts/README.md)