Automatically build UI before compiling

pio-scripts/build_ui.py

@@ -0,0 +1,3 @@
+Import('env')
+
+env.Execute("npm run build")

platformio.ini

@@ -155,6 +155,7 @@ extra_scripts =
   post:pio-scripts/output_bins.py
   post:pio-scripts/strip-floats.py
   pre:pio-scripts/user_config_copy.py
+  pre:pio-scripts/build_ui.py
 
 # ------------------------------------------------------------------------------
 # COMMON SETTINGS: