feat: auto-start stopped containers on boot, add failure recovery tests

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>

core/archipelago/src/main.rs

@@ -76,6 +76,15 @@ async fn main() -> Result<()> {
         );
     }
 
+    // Start any stopped containers (handles clean reboot where PID was removed)
+    let boot_report = crash_recovery::start_stopped_containers().await;
+    if boot_report.total > 0 {
+        info!(
+            "🔄 Boot startup: {}/{} containers started (failed: {:?})",
+            boot_report.recovered, boot_report.total, boot_report.failed
+        );
+    }
+
     // Write PID marker so we can detect crashes on next startup
     crash_recovery::write_pid_marker(&config.data_dir).await?;