feat(lighting): add backlight behavior

app/Kconfig

@@ -257,7 +257,7 @@ menu "Display/LED Options"
 
 rsource "src/display/Kconfig"
 
-config ZMK_RGB_UNDERGLOW
+menuconfig ZMK_RGB_UNDERGLOW
 	bool "RGB Adressable LED Underglow"
 	select LED_STRIP
 
@@ -328,6 +328,39 @@ config ZMK_RGB_UNDERGLOW_ON_START
 #ZMK_RGB_UNDERGLOW
 endif
 
+menuconfig ZMK_BACKLIGHT
+	bool "LED backlight"
+	select PWM
+	select LED
+	select ZMK_LED_PWM
+
+if ZMK_BACKLIGHT
+
+config ZMK_BACKLIGHT_BRT_STEP
+	int "Brightness step in percent"
+	range 1 100
+	default 20
+
+config ZMK_BACKLIGHT_BRT_START
+	int "Default brightness in percent"
+	range 1 100
+	default 40
+
+config ZMK_BACKLIGHT_ON_START
+	bool "Default backlight state"
+	default y
+
+config ZMK_BACKLIGHT_AUTO_OFF_IDLE
+	bool "Turn off backlight when keyboard goes into idle state"
+	default y
+
+config ZMK_BACKLIGHT_AUTO_OFF_USB
+	bool "Turn off backlight when USB is disconnected"
+	default n
+
+#ZMK_BACKLIGHT
+endif
+
 #Display/LED Options
 endmenu
 
@@ -378,7 +411,7 @@ config ZMK_COMBO_MAX_KEYS_PER_COMBO
 	int "Maximum number of keys per combo"
 	default 4
 
-#Display/LED Options
+#Combo options
 endmenu
 
 menu "Advanced"