fix(shields): Load Kconfig for out-of-tree shields

app/Kconfig

@@ -193,6 +193,10 @@ source "subsys/logging/Kconfig.template.log_config"
 
 rsource "boards/Kconfig"
 rsource "boards/shields/*/Kconfig.defconfig"
+rsource "boards/shields/*/Kconfig.shield"
+
+osource "$(ZMK_CONFIG)/boards/shields/*/Kconfig.defconfig"
+osource "$(ZMK_CONFIG)/boards/shields/*/Kconfig.shield"
 
 source "Kconfig.zephyr"
 

app/cmake/zmk_config.cmake

@@ -44,6 +44,7 @@ endif()
 set(CACHED_ZMK_CONFIG ${ZMK_CONFIG} CACHE STRING "Selected user ZMK config")
 
 if (ZMK_CONFIG)
+	set(ENV{ZMK_CONFIG} "${ZMK_CONFIG}")
 	if(EXISTS ${ZMK_CONFIG}/boards)
 		message(STATUS "Adding ZMK config directory as board root: ${ZMK_CONFIG}")
 		list(APPEND BOARD_ROOT ${ZMK_CONFIG})