Permissions: Fix What's Broken

Three things on this box are failing, and every one is a permissions problem. Diagnose with ls -l / stat, then fix:

1. 'The nightly backup never runs.' — /root/app/backup.sh exists and cron calls it (/etc/cron.d/nightly-backup, as root), but look at its mode. Make it runnable without making it writable by others: a script root runs on a schedule must not be editable by every user.

2. 'Anyone can edit our config!' — /root/app/config.ini is world-writable. Lock it to owner read/write + group read (640).

3. 'ssh refuses our deploy key.' — ssh will not use a private key that others can read. /root/keys/deploy_key must be mode 600.

This is the everyday troubleshooting loop: symptom → inspect the mode → chmod the fix.