Fix 3.5" black screen: drive backlight on GPIO27, not GPIO21.

GPIO21 is GT911 INT on 3248S035C; PWM on the wrong pin left the panel dark.

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

src/touch.cpp

@@ -76,9 +76,8 @@ static void gt_hw_reset(bool addr_0x14) {
   delay(5);
   digitalWrite(CYD_GT911_INT, LOW);
   delay(50);
-  /* INT shares TFT_BL on 3.5 — keep backlight HIGH after address select. */
-  pinMode(CYD_GT911_INT, OUTPUT);
-  digitalWrite(CYD_GT911_INT, HIGH);
+  /* Backlight is GPIO27 — leave INT as input for polling / optional IRQ. */
+  pinMode(CYD_GT911_INT, INPUT);
   delay(50);
 }