refactor(boards): Move mikoto to ZMK variant by default

Make the standard mikoto board ID be `mikoto/nrf52840/zmk` or
`mikoto//zmk` by shorthand.

app/boards/zhiayang/mikoto/Kconfig.mikoto

@@ -3,7 +3,7 @@
 
 config BOARD_MIKOTO
     select SOC_NRF52840_QIAA
-    imply RETAINED_MEM
-    imply RETENTION
-    imply RETENTION_BOOT_MODE
+    imply RETAINED_MEM if BOARD_MIKOTO_NRF52840_ZMK
+    imply RETENTION if BOARD_MIKOTO_NRF52840_ZMK
+    imply RETENTION_BOOT_MODE if BOARD_MIKOTO_NRF52840_ZMK
     imply I2C if BOARD_REVISION="7.2.0"

app/boards/zhiayang/mikoto/board.yml

@@ -1,14 +1,5 @@
 board:
-  name: mikoto
-  vendor: zhiayang
-  revision:
-    format: major.minor.patch
-    default: 5.20.0
-    exact: false
-    revisions:
-      - name: 5.20.0
-      - name: 6.1.0
-      - name: 6.3.0
-      - name: 7.2.0
-  socs:
-    - name: nrf52840
+  extend: mikoto
+  variants:
+    - name: zmk
+      qualifier: nrf52840

app/boards/zhiayang/mikoto/mikoto.zmk.yml

@@ -1,5 +1,5 @@
 file_format: "1"
-id: mikoto
+id: mikoto//zmk
 name: Mikoto
 type: board
 arch: arm

app/boards/zhiayang/mikoto/mikoto_nrf52840_zmk.dts

@@ -0,0 +1,28 @@
+/*
+ * Copyright (c) 2026 The ZMK Contributors
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+#include <../boards/zhiayang/mikoto/mikoto.dts>
+#include <common/nordic/nrf52840_uf2_boot_mode.dtsi>
+
+/ {
+    chosen {
+        zmk,battery = &vbatt;
+    };
+
+    // Node name must match original "EXT_POWER" label to preserve user settings.
+    EXT_POWER {
+        compatible = "zmk,ext-power-generic";
+        control-gpios = <&gpio0 13 GPIO_ACTIVE_HIGH>;
+        init-delay-ms = <50>;
+    };
+
+    vbatt: vbatt {
+        compatible = "zmk,battery-voltage-divider";
+        io-channels = <&adc 1>;
+        output-ohms = <10000000>;
+        full-ohms = <(10000000 + 4000000)>;
+    };
+};

app/boards/zhiayang/mikoto/mikoto_nrf52840_zmk_5_20_0.overlay

@@ -0,0 +1,8 @@
+/*
+ * Copyright (c) 2026 The ZMK Contributors
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+#include <../boards/zhiayang/mikoto/mikoto-pinctrl.dtsi>
+#include <../boards/zhiayang/mikoto/arduino_pro_micro_pins_v5.dtsi>

app/boards/zhiayang/mikoto/mikoto_nrf52840_zmk_6_1_0.overlay

@@ -0,0 +1,8 @@
+/*
+ * Copyright (c) 2026 The ZMK Contributors
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+#include <../boards/zhiayang/mikoto/mikoto-pinctrl.dtsi>
+#include <../boards/zhiayang/mikoto/arduino_pro_micro_pins_v5.dtsi>

app/boards/zhiayang/mikoto/mikoto_nrf52840_zmk_7_2_0.overlay

@@ -0,0 +1,47 @@
+/*
+ * Copyright (c) 2026 The ZMK Contributors
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+#include <../boards/zhiayang/mikoto/mikoto-pinctrl.dtsi>
+#include <../boards/zhiayang/mikoto/arduino_pro_micro_pins_v6.dtsi>
+
+&pinctrl {
+    i2c1_default: i2c1_default {
+        group1 {
+            psels = <NRF_PSEL(TWIM_SDA, 0, 23)>,
+                    <NRF_PSEL(TWIM_SCL, 0, 19)>;
+            bias-pull-up;
+        };
+    };
+
+    i2c1_sleep: i2c1_sleep {
+        group1 {
+            psels = <NRF_PSEL(TWIM_SDA, 0, 23)>,
+                    <NRF_PSEL(TWIM_SCL, 0, 19)>;
+            low-power-enable;
+            bias-pull-up;
+        };
+    };
+};
+
+&i2c1 {
+    status = "okay";
+    compatible = "nordic,nrf-twi";
+    pinctrl-0 = <&i2c1_default>;
+    pinctrl-1 = <&i2c1_sleep>;
+    pinctrl-names = "default", "sleep";
+
+    builtin_fuel_gauge: max17048@36 {
+        compatible = "zmk,maxim-max17048";
+        status = "okay";
+        reg = <0x36>;
+    };
+};
+
+/ {
+    chosen {
+        zmk,battery = &builtin_fuel_gauge;
+    };
+};

app/module/boards/zhiayang/mikoto/Kconfig.defconfig

@@ -15,9 +15,6 @@ config USB_DEVICE_STACK
 
 endif # USB
 
-config BT_CTLR
-    default BT
-
 choice BOARD_MIKOTO_CHARGER_CURRENT
     default BOARD_MIKOTO_CHARGER_CURRENT_100MA
 endchoice

app/module/boards/zhiayang/mikoto/Kconfig.mikoto

@@ -0,0 +1,5 @@
+# Copyright (c) 2026 The ZMK Contributors
+# SPDX-License-Identifier: Apache-2.0
+
+config BOARD_MIKOTO
+    select SOC_NRF52840_QIAA

app/module/boards/zhiayang/mikoto/board.cmake

@@ -0,0 +1,5 @@
+# SPDX-License-Identifier: MIT
+
+board_runner_args(nrfjprog "--nrf-family=NRF52" "--softreset")
+include(${ZEPHYR_BASE}/boards/common/uf2.board.cmake)
+include(${ZEPHYR_BASE}/boards/common/nrfjprog.board.cmake)

app/module/boards/zhiayang/mikoto/board.yml

@@ -0,0 +1,14 @@
+board:
+  name: mikoto
+  vendor: zhiayang
+  revision:
+    format: major.minor.patch
+    default: 5.20.0
+    exact: false
+    revisions:
+      - name: 5.20.0
+      - name: 6.1.0
+      - name: 6.3.0
+      - name: 7.2.0
+  socs:
+    - name: nrf52840

app/module/boards/zhiayang/mikoto/mikoto.dts

@@ -16,7 +16,6 @@
         zephyr,code-partition = &code_partition;
         zephyr,sram = &sram0;
         zephyr,flash = &flash0;
-        zmk,battery = &vbatt;
     };
 
     leds {
@@ -25,20 +24,6 @@
             gpios = <&gpio0 15 GPIO_ACTIVE_HIGH>;
         };
     };
-
-    // Node name must match original "EXT_POWER" label to preserve user settings.
-    EXT_POWER {
-        compatible = "zmk,ext-power-generic";
-        control-gpios = <&gpio0 13 GPIO_ACTIVE_HIGH>;
-        init-delay-ms = <50>;
-    };
-
-    vbatt: vbatt {
-        compatible = "zmk,battery-voltage-divider";
-        io-channels = <&adc 1>;
-        output-ohms = <10000000>;
-        full-ohms = <(10000000 + 4000000)>;
-    };
 };
 
 &reg1 {

app/module/boards/zhiayang/mikoto/mikoto_7_2_0.conf

@@ -0,0 +1,2 @@
+CONFIG_I2C=y
+CONFIG_ZMK_MAX17048=y

app/module/boards/zhiayang/mikoto/mikoto_defconfig

@@ -0,0 +1,12 @@
+# SPDX-License-Identifier: MIT
+
+# Enable MPU
+CONFIG_ARM_MPU=y
+CONFIG_PINCTRL=y
+
+# enable GPIO
+CONFIG_GPIO=y
+
+CONFIG_USE_DT_CODE_PARTITION=y
+CONFIG_BUILD_OUTPUT_UF2=y
+

app/module/boards/zhiayang/mikoto/pre_dt_board.cmake

@@ -0,0 +1,8 @@
+# Copyright (c) 2026 The ZMK Contributors
+# SPDX-License-Identifier: MIT
+#
+
+# Suppresses duplicate unit-address warning at build time for power, clock, acl and flash-controller
+# https://docs.zephyrproject.org/latest/build/dts/intro-input-output.html
+
+list(APPEND EXTRA_DTC_FLAGS "-Wno-unique_unit_address_if_enabled")