Add Elecrow ThinkNode M4 variant (nRF52840 + LR1110)

[M0JSX]

Adds MeshCore companion BLE, repeater, and room server firmware support for the Elecrow ThinkNode M4 — a power bank device with integrated LoRa communication, GPS, and nRF52840 + Semtech LR1110.
Hardware:

MCU: Nordic nRF52840
Radio: Semtech LR1110 (868/915 MHz)
GPS: Quectel L76K
Battery: 2x18650 parallel (~7000mAh)
Bootloader: UF2, SoftDevice S140 v6.1.1

Environments:

ThinkNode_M4_companion_ble — BLE companion radio (PIN: 123456)
ThinkNode_M4_repeater — standalone repeater
ThinkNode_M4_room_server — standalone room server

Features implemented:

BLE advertising, pairing and secure connection
LoRa messaging via LR1110
GPS via L76K (enable/disable via settings)
Battery percentage and voltage via power bank serial chip (UART at 4800 baud, pins RX=30, TX=5)
Battery gauge LEDs — show level on button press for 10 seconds
LoRa TX/RX blue LED flash
Power-on red LED sequence — 3 quick flashes then steady during init
Sleep on 3s long press, wake on button press
Double press sends location advert

Key implementation notes:

LED_BLUE must be set to -1 — without this Bluefruit calls digitalWrite(41) continuously during BLE advertising, causing random hard fault crashes
Serial2 instead of SoftwareSerial — SoftwareSerial interrupt conflicts with the SoftDevice S140 causing random crashes; hardware UART (NRF_UARTE1) on pins 30/5 is stable
SoftDevice v6.1.1 required — must match the factory bootloader; v7 causes RADIOLIB_ERR_CHIP_NOT_FOUND
RadioLib must be pinned to 7.6.0 — v7.7.1 returns RADIOLIB_ERR_SPI_CMD_INVALID (-706) with the LR1110 firmware on this hardware
Power enable pins must be driven before radio SPI init: PIN_POWER_EN (11) HIGH and VEXT_ENABLE (32) LOW
RF switch table uses only DIO5/DIO6 with 2 values, matching Meshtastic's rfswitch.h for this board
PIN_SERIAL2_RX=30 / PIN_SERIAL2_TX=5 must be defined in variant.h to enable hardware Serial2 for the battery management chip
board.loop() is called from ThinkNodeM4SensorManager::loop() since the main loop only calls sensors.loop()
lib/nrf52/s140_nrf52_6.1.1_API must be copied from the PlatformIO framework packages before building:

bash cp -r ~/.platformio/packages/framework-arduinoadafruitnrf52/cores/nRF5/nordic/softdevice/s140_nrf52_6.1.1_API lib/nrf52/
Pin mapping (from Meshtastic variants/nrf52840/ELECROW-ThinkNode-M4/variant.h):

SPI: MISO=8, MOSI=7, SCK=6, NSS=27
LR1110: RESET=40 (P1.08), IRQ=12, BUSY=26
GPS: EN=43 (P1.11, active LOW), RESET=3, STANDBY=28, RX=46 (P1.14), TX=44 (P1.12)
Battery LEDs: 15, 17, 34 (P1.02), 36 (P1.04)
Battery serial: RX=30, TX=5, 4800 baud
Power: PIN_POWER_EN=11 (HIGH=on), VEXT_ENABLE=32/P1.00 (LOW=on)
Button: 4, LED_HEARTBEAT=41 (P1.09, red), LED_PAIRING=13 (blue)

Known limitations:

Battery percentage from serial chip may differ slightly from app-displayed value — the power bank chip reports per-cell voltage; the app uses its own voltage-to-percentage curve
GPS LED breathing/pulse effect not yet implemented

Tested on: Elecrow ThinkNode M4 (LMM14004D1), EU 868MHz — BLE advertising, pairing, LoRa messaging, battery display, LED indicators and sleep/wake all confirmed working.