cmd/pkgserver: guard sass/ts behind build tag

Packaging nodejs and ruby is an immense burden for the Rosa OS base system, and these files diff poorly.

Signed-off-by: Ophestra <cat@gensokyo.uk>

cmd/pkgserver/ui_full.go

@@ -0,0 +1,7 @@
+//go:build frontend
+
+package main
+
+//go:generate sh -c "sass ui/static/dark.scss ui/static/dark.css && sass ui/static/light.scss ui/static/light.css && tsc -p ui/static"
+//go:embed ui/*
+var content embed.FS