Added start_stopped_containers() to crash_recovery.rs that starts all
exited/created containers on backend startup, fixing the issue where
containers didn't come back after clean reboot (PID marker removed by
systemd stop). Created test-failure-recovery.sh covering 5 failure
scenarios: container crash, backend restart, Tor restart, full reboot,
and Tor traffic block (UPTIME-02).
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
