Update ATtiny84 firmware to use Volume Up for shutdown, configure KeyMapper, and document automatic boot hotspot

Arduino/LIN_to_IR/LIN_to_IR.cpp

@@ -85,7 +85,7 @@ uint32_t get_mce_code(uint8_t button) {
     case 4: return 0x800f0421; // RIGHT
     case 5: return 0x800f0422; // ENTER / OK
     case 6: return 0x800f0423; // BACK
-    case 7: return 0x800f046f; // F12 (Shutdown)
+    case 7: return 0x800f0410; // Volume Up (Shutdown)
     default: return 0;
   }
 }
@@ -210,7 +210,7 @@ void loop() {
     current_button = 0;
   }
 
-  // Car off detection: if no LIN activity for 5 seconds, send F12 to trigger shutdown
+  // Car off detection: if no LIN activity for 5 seconds, send Volume Up to trigger shutdown
   if (is_car_on && (millis() - last_lin_activity_time > 5000)) {
     is_car_on = false;
     for (int i = 0; i < 3; i++) {