Each rule group now shows which root is the type's default ('Default:
{root} — unmatched downloads go here'), and the default root's option in
the per-rule root dropdown carries a '(default)' suffix. Comparison is
deliberately loose (separators, trailing slashes, case) since this is
display-only. Changing a default root select in the Library section
re-renders the rules editor so the cue never goes stale.