feat(backup): add Restic S3 backup recipes

Introduce comprehensive recipes for Restic-based S3 backups.
Covers installation, S3 repository configuration, automated backup job creation, and restoration of files.

recipes/backup/03_create-backup-job.md

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+# Create Automatic Backup Job
+
+This recipe creates a daily backup job using Restic and systemd.
+
+## Create Backup Script
+
+```bash
+sudo nano /usr/local/bin/restic-backup.sh
+```
+
+Contents:
+
+```bash
+#!/usr/bin/env bash
+set -e
+
+source /etc/restic.env
+
+restic backup <PATH>
+
+restic forget --keep-daily 7 --keep-weekly 4 --keep-monthly 12 --keep-yearly 3 --prune
+```
+
+Replace:
+
+- `<PATH>` with the folder path you want to backup (e.g. `/srv/samba`)
+
+## Make Script Executable
+
+```bash
+sudo chmod +x /usr/local/bin/restic-backup.sh
+```
+
+## Load Environment
+
+```bash
+source <(sudo cat /etc/restic.env)
+```
+
+## Test Backup
+
+```bash
+sudo /usr/local/bin/restic-backup.sh
+```
+
+## Verify Snapshot
+
+```bash
+restic snapshots
+```
+
+Expected output:
+
+```text
+ID        Time                 Host
+----------------------------------------
+xxxxxxxx  YYYY-MM-DD HH:MM     hostname
+```
+
+## Automate with Cron
+
+Edit root crontab.
+
+```bash
+sudo crontab -e
+```
+
+Add:
+
+```cron
+0 2 * * * /usr/local/bin/restic-backup.sh
+```
+
+## Verify Cron
+
+```bash
+sudo crontab -l
+```
+
+Expected output should contain:
+
+```cron
+0 2 * * * /usr/local/bin/restic-backup.sh
+```
+
+## Troubleshooting
+
+### Repository not found
+
+Verify:
+
+```bash
+echo $RESTIC_REPOSITORY
+```
+
+### Authentication failed
+
+Verify the configured S3 credentials.
+
+```bash
+echo $AWS_ACCESS_KEY_ID
+```
+
+```bash
+echo $AWS_SECRET_ACCESS_KEY
+```
+
+### Wrong password
+
+Verify:
+
+```bash
+echo $RESTIC_PASSWORD
+```