Add Elecrow ThinkNode M8 board support (thinknode_m8) (#11226)

* Add Elecrow ThinkNode M8 variant scaffold (thinknode_m8)

nRF52840 + SX1262 + 2.4" e-paper + ATGM336H-5NR32 GPS.
All pins resolved from ThinkNode_M8_V0.3.sch; cross-checked
against meshtastic/firmware#9181 (Elecrow V0.1 reference).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* Add Elecrow ThinkNode M8 board support (nRF52840/SX1262, 1.54in e-ink, ATGM336H GNSS, SC7A20, EC04 encoder)

* Address review: keep the stored backlight level out of blanking, match only the SC7A20 WHO_AM_I byte, and transfer detents atomically

* Use std::atomic for the press-and-turn detent counter so native builds compile

* Drop the ThinkNode M8 LED_BUILTIN redefinition that warned on every translation unit

---------

Co-authored-by: claude[bot] <41898282+claude[bot]@users.noreply.github.com>
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

src/motion/AccelerometerThread.h

@@ -106,6 +106,7 @@ class AccelerometerThread : public concurrency::OSThread
             break;
 #if __has_include(<Adafruit_LIS3DH.h>)
         case ScanI2C::DeviceType::LIS3DH:
+        case ScanI2C::DeviceType::SC7A20:
             sensor = new LIS3DHSensor(device);
             break;
 #endif