fix buttons working, add basic brightness control

firmware/app/main.c

@@ -27,6 +27,7 @@
 #include "led/ledprog.h"
 
 #include "ui/btn.h"
+#include "ui/temp_ui.h"
 
 /*
  *@Note
@@ -162,6 +163,9 @@ int main(void)
     // set up accelerometer
     spim_init();
 
+    // set up user interface
+    tempui_init();
+
     // configure AWU to provide ~997Hz wakeup interrupt for main program
     // TODO: confirm if the counter is reset / preloaded
     awu_init();