feat: Add Inhero MR-2 repeater variant

Hardware: RAK4630, BQ25798 MPPT solar charger with Power Path, INA228 fuel gauge, RV-3028-C7 RTC, BME280.

Features:
- Multi-chemistry support: Li-Ion, LiFePO4, LTO, Na-Ion with JEITA
- 3.6-24V MPPT solar charging
- Precision fuel gauging via INA228 (coulomb counting + voltage correlation)
- Low-power: ~6 mA active idle (RX), < 500 uA sleep, ~15 uA system-off
- Low V Sleep with RTC-triggered recovery checks
- Configuration via custom CLI commands via get/set board.* extension pattern

Includes: board definition, variant config, I2C drivers (BQ25798, INA228),
BoardConfigContainer.

Author: liekmarflow

boards/inhero_mr2.json

@@ -0,0 +1,74 @@
+{
+  "build": {
+    "arduino": {
+      "ldscript": "nrf52840_s140_v6.ld"
+    },
+    "core": "nRF5",
+    "cpu": "cortex-m4",
+    "extra_flags": "-DARDUINO_NRF52840_FEATHER -DNRF52840_XXAA",
+    "f_cpu": "64000000L",
+    "hwids": [
+      [
+        "0x239A",
+        "0x8029"
+      ],
+      [
+        "0x239A",
+        "0x0029"
+      ],
+      [
+        "0x239A",
+        "0x002A"
+      ],
+      [
+        "0x239A",
+        "0x802A"
+      ]
+    ],
+    "usb_product": "Inhero MR2",
+    "mcu": "nrf52840",
+    "variant": "Inhero_MR2_Board",
+    "bsp": {
+      "name": "adafruit"
+    },
+    "softdevice": {
+      "sd_flags": "-DS140",
+      "sd_name": "s140",
+      "sd_version": "6.1.1",
+      "sd_fwid": "0x00B6"
+    },
+    "bootloader": {
+      "settings_addr": "0xFF000"
+    }
+  },
+  "connectivity": [
+    "bluetooth"
+  ],
+  "debug": {
+    "jlink_device": "nRF52840_xxAA",
+    "svd_path": "nrf52840.svd",
+    "openocd_target": "nrf52.cfg"
+  },
+  "frameworks": [
+    "arduino"
+  ],
+  "name": "Inhero MR-2",
+  "upload": {
+    "maximum_ram_size": 235520,
+    "maximum_size": 815104,
+    "speed": 115200,
+    "protocol": "nrfutil",
+    "protocols": [
+      "jlink",
+      "nrfjprog",
+      "nrfutil",
+      "stlink",
+      "cmsis-dap"
+    ],
+    "use_1200bps_touch": true,
+    "require_upload_port": true,
+    "wait_for_upload_port": true
+  },
+  "url": "https://inhero.de",
+  "vendor": "Inhero GmbH"
+}