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().

examples/companion_radio/ui-new/UITask.cpp

@@ -2346,6 +2346,7 @@ void UITask::loop() {
       case KEY_DOWN:  enqueueKey(checkDisplayOn(KEY_DOWN));  break;
       case KEY_CANCEL:enqueueKey(checkDisplayOn(KEY_CANCEL));break;
       case KEY_HOME:
+        checkDisplayOn(k);   // wake/extend same as every other key here, even though Home has no nav action
         #ifdef LILYGO_TECHO_LITE_KEYSHIELD
         extern void techo_keyshield_backlight_toggle();
         techo_keyshield_backlight_toggle();