refactor(doorbell): migrate ESP32-S3 to ESP_IOExpander library

sketches/doorbell-touch/DisplayManager.cpp

@@ -22,8 +22,10 @@ void DisplayManager::begin() {
 #endif
 }
 
-void DisplayManager::setBacklight(bool on) {
-  digitalWrite(PIN_LCD_BL, on ? HIGH : LOW);
+void DisplayDriverGFX::setBacklight(bool on) {
+    // Cannot control after gfx->begin() — GPIO 8/9 are LCD data.
+    // Backlight is permanently ON, set during ch422gInit().
+    (void)on;
 }
 
 TouchEvent DisplayManager::readTouch() {