v0.2.0 — Monitoring, security reporting, and cron auditing

New scripts (4):
- disk/disk-alert.sh           — disk usage monitor with warn/crit thresholds
- monitoring/service-watchdog.sh — auto-restart downed systemd services
- security/fail2ban-report.sh  — attack summary, top offenders, recent bans
- cron/cron-audit.sh           — all scheduled jobs in one unified view

Bug fixes:
- ssl/ssl-expiry-check.sh: fixed silent exit on unreachable domains (set -e + pipeline)

Docs:
- Improved README: ToC, real curl commands, status table, script template
- Added CONTRIBUTING.md with script requirements and review expectations

Tested on: Ubuntu 22.04 LTS, Ubuntu 24.04 LTS