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/graphics/draw/MenuHandler.cpp

@@ -10,6 +10,7 @@
 #include "MessageStore.h"
 #include "NodeDB.h"
 #include "buzz.h"
+#include "graphics/Backlight.h"
 #include "graphics/Screen.h"
 #include "graphics/SharedUIDisplay.h"
 #include "graphics/TFTColorRegions.h"
@@ -1108,7 +1109,7 @@ void menuHandler::homeBaseMenu()
         }
         optionsEnumArray[options++] = Mute;
     }
-#if defined(PIN_EINK_EN) || defined(PCA_PIN_EINK_EN)
+#if HAS_PWM_BACKLIGHT || defined(PIN_EINK_EN) || defined(PCA_PIN_EINK_EN)
     optionsArray[options] = "Toggle Backlight";
     optionsEnumArray[options++] = Backlight;
 #else
@@ -1138,7 +1139,10 @@ void menuHandler::homeBaseMenu()
             }
         } else if (selected == Backlight) {
             screen->setOn(false);
-#if defined(PIN_EINK_EN)
+#if HAS_PWM_BACKLIGHT
+            graphics::backlightToggle();
+            saveUIConfig();
+#elif defined(PIN_EINK_EN)
             if (uiconfig.screen_brightness == 1) {
                 uiconfig.screen_brightness = 0;
                 digitalWrite(PIN_EINK_EN, LOW);