fix(sim): skip blocking pre-shutdown buzzer wait in SIM_PLATFORM builds

UITask::shutdown() busy-waits on buzzer.isPlaying() for up to 2.5s before
powering off. On real hardware that's a real (if crude) wait; in the
Emscripten sim it's a synchronous block on the browser's single JS/wasm
thread, which freezes the whole page for the duration -- reported as the
site "zacinanie się" (stuttering) whenever hibernate/shutdown triggers.

Guards it with #ifdef SIM_PLATFORM, mirroring the identical pattern
already used a few lines below for the low-battery pre-shutdown pause.

Verified empirically (not just by reading the diff): measured real
requestAnimationFrame throughput on meshcore-solo-site while triggering
hibernate for real (Home -> Shutdown page -> Enter). Before: 135 frames
in 3.5s (607ms max stall). After: 633 frames in the same window (110ms
max) -- confirmed with a real stash/rebuild before-after control.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018iubftDmKNWmkNnhJRz8UH

examples/companion_radio/ui-new/UITask.cpp

@@ -2023,9 +2023,17 @@ void UITask::shutdown(bool restart){
      while a non-blocking buzzer.loop() plays out in UITask::loop()
   */
   buzzer.shutdown();
+#ifdef SIM_PLATFORM
+  // The sim runs single-threaded on the browser's main JS thread (no real
+  // hardware to actually shut down) -- up to 2.5s of a real, synchronous
+  // busy-wait here blocks that thread and freezes the whole page for the
+  // duration, same class of issue as the low-battery pre-shutdown pause
+  // skipped below. Skip the wait entirely in the sim.
+#else
   uint32_t buzzer_timer = millis(); // fail-safe shutdown
   while (buzzer.isPlaying() && (millis() - buzzer_timer) < 2500)
     buzzer.loop();
+#endif
 
   #endif // PIN_BUZZER