Add touch buttons for speaker toggle and music playback.

Enable SoftSPI touch, replace auto beeps with Speaker ON/OFF and Play Music controls, and document usage.

Co-authored-by: Cursor <cursoragent@cursor.com>

include/ui.h

@@ -4,4 +4,4 @@
 
 void ui_create();
 void ui_update(const SdCardInfo &info);
-void ui_set_audio_status(const char *text);
+void ui_refresh_audio_buttons();