fix(ui): wake display on T-Echo KeyShield Home key, drop dead code

Home key toggles the keyboard backlight but wasn't going through
checkDisplayOn() like every other TCA8418 key, so it couldn't wake a
sleeping display or extend the auto-off timer.

Also: removed a no-op #elif branch in ST7789Display.cpp (same values as
the #else it duplicated), and ENABLE_SCREENSHOT on the Cardputer ADV
solo env, which does nothing since ST7789Display has no getBuffer().

src/helpers/ui/ST7789Display.cpp

@@ -18,11 +18,8 @@
 #ifdef HELTEC_VISION_MASTER_T190
   #define SCALE_X  2.5f        // 320 / 128
   #define SCALE_Y  2.65625f    // 170 / 64
-#elif defined(CARDPUTER_ADV)
-  #define SCALE_X  1.875f      // 240 / 128
-  #define SCALE_Y  2.109375f   // 135 / 64
 #else
-  #define SCALE_X  1.875f      // 240 / 128
+  #define SCALE_X  1.875f      // 240 / 128 -- also Cardputer ADV's panel, same resolution
   #define SCALE_Y  2.109375f   // 135 / 64
 #endif