feat: reboot button in Settings with password confirmation

- system.reboot RPC endpoint requires password re-verification
- Uses systemd path unit pattern (tor-helper.sh) for privilege escalation
- 2-second delay before reboot to allow RPC response to reach client
- Clean UI: password input modal, loading state, error feedback

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

core/archipelago/src/api/rpc/mod.rs

@@ -705,6 +705,7 @@ impl RpcHandler {
             "system.detect-usb-devices" => self.handle_system_detect_usb_devices().await,
             "system.disk-status" => self.handle_system_disk_status().await,
             "system.disk-cleanup" => self.handle_system_disk_cleanup().await,
+            "system.reboot" => self.handle_system_reboot(params).await,
             "system.factory-reset" => self.handle_system_factory_reset(params).await,
 
             // Opt-in anonymous analytics