wt2: shared PWM brightness for the status LED (heartbeat/TX/flashes)

Ports the T096 "Option 1" design (single LED, get/set leds on|off
persisted + get/set leds.brightness 0-100 RAM-only) to the Wireless
Tracker V2, which has the same single-LED-multi-purpose situation
(status_led doubles as heartbeat/message-flash/shutdown-flash/TX
indicator, same as T096's P0.28).

Adds a new ledc0 PWM channel on GPIO18 (same physical pin as the
existing plain-GPIO status_led) with heartbeat-pwm-led/lora-tx-pwm-led
aliases -- the shared C++ logic (helpers/ui/ui_common.c,
adapters/board/ZephyrBoard.cpp, helpers/led_gate.c/h,
helpers/CommonCLI.cpp) already existed from the T096 commits and needed
no changes, being board-agnostic behind DT_NODE_EXISTS checks.

CONFIG_PWM=y deliberately NOT in the board defconfig: WT2 builds via
--sysbuild (mcuboot + app as two images sharing that defconfig), and
mcuboot's minimal kernel config has no k_sem_give()/k_sem_take(), which
the ESP32 PWM LED driver needs -- CONFIG_PWM=y there links the app image
fine but fails mcuboot's link. New boards/common/esp32s3_pwm_led.conf
scopes it to the app image only via EXTRA_CONF_FILE, alongside the
existing esp32s3_usb.conf.

zephcore/boards/common/esp32s3_pwm_led.conf

@@ -0,0 +1,15 @@
+# Enable PWM on ESP32-S3 sysbuild targets (shared heartbeat/TX LED brightness,
+# see the heartbeat-pwm-led / lora-tx-pwm-led devicetree aliases consumed by
+# helpers/ui/ui_common.c and adapters/board/ZephyrBoard.cpp).
+#
+# Deliberately NOT in the board *_defconfig: that file is shared by every
+# sysbuild image for the board, including mcuboot, whose minimal kernel
+# config has no k_sem_give()/k_sem_take() -- CONFIG_PWM=y there links fine for
+# the app image but fails mcuboot's link with "undefined reference to
+# z_impl_k_sem_give/take" (drivers/pwm/pwm_led_esp32.c uses a semaphore).
+# EXTRA_CONF_FILE scopes this to the app ("zephcore") image only.
+#
+# Build with:
+#   -DEXTRA_CONF_FILE="boards/common/esp32s3_usb.conf;boards/common/esp32s3_pwm_led.conf"
+
+CONFIG_PWM=y

zephcore/boards/esp32/heltec_wireless_tracker_v2/heltec_wireless_tracker_v2-pinctrl.dtsi

@@ -72,4 +72,11 @@
 			output-low;
 		};
 	};
+
+	ledc0_default: ledc0_default {
+		group1 {
+			pinmux = <LEDC_CH0_GPIO18>;
+			output-enable;
+		};
+	};
 };

zephcore/boards/esp32/heltec_wireless_tracker_v2/heltec_wireless_tracker_v2_procpu.dts

@@ -30,6 +30,7 @@
 #include <zephyr/dt-bindings/input/input-event-codes.h>
 #include <zephyr/dt-bindings/lora/sx126x.h>
 #include <zephyr/dt-bindings/gpio/espressif-esp32-gpio.h>
+#include <zephyr/dt-bindings/pwm/pwm.h>
 #include "heltec_wireless_tracker_v2-pinctrl.dtsi"
 
 / {
@@ -39,6 +40,8 @@
 	aliases {
 		led0 = &status_led;
 		lora-tx-led = &status_led;
+		heartbeat-pwm-led = &pwm_status_led;
+		lora-tx-pwm-led = &pwm_status_led;
 		uart-0 = &uart0;
 		uart-2 = &uart2;
 		i2c-0 = &i2c0;
@@ -69,6 +72,22 @@
 		};
 	};
 
+	/* Same GPIO18 net as status_led above, driven through the LEDC PWM
+	 * peripheral instead of a raw GPIO write. Single LED doubling as
+	 * heartbeat, message/shutdown flash and LoRa TX indicator (same
+	 * "Option 1" shared-brightness pattern as T096, see helpers/ui/ui_common.c
+	 * and adapters/board/ZephyrBoard.cpp: heartbeat-pwm-led/lora-tx-pwm-led
+	 * aliases give every one of those events a single 0-100 brightness knob,
+	 * RAM-only, on top of the existing persisted on/off gate. */
+	pwm_leds {
+		compatible = "pwm-leds";
+
+		pwm_status_led: pwm_led_gpio18 {
+			label = "Status PWM LED";
+			pwms = <&ledc0 0 PWM_MSEC(10) PWM_POLARITY_NORMAL>;
+		};
+	};
+
 	buttons: buttons {
 		compatible = "gpio-keys";
 
@@ -231,6 +250,19 @@
 	status = "okay";
 };
 
+&ledc0 {
+	pinctrl-0 = <&ledc0_default>;
+	pinctrl-names = "default";
+	status = "okay";
+	#address-cells = <1>;
+	#size-cells = <0>;
+
+	channel0@0 {
+		reg = <0x0>;
+		timer = <0>;
+	};
+};
+
 &i2c0 {
 	status = "okay";
 	clock-frequency = <I2C_BITRATE_FAST>;