feat: disconnect Bluetooth devices, flush disks on shutdown/reboot, display progress in login.elf window

programs/src/shutdown/main.cpp

@@ -8,5 +8,8 @@
 
 extern "C" void _start() {
     montauk::print("Shutting down...\n");
+    // This low-level utility bypasses the login graceful-shutdown view, so flush
+    // pending writes and unmount disk-backed volumes here before powering off.
+    montauk::fs_sync();
     montauk::shutdown();
 }