Tracks whether any upgrade section has printed content yet, so a run
covering several optional sections (shell presets, app configs, managed
system configs) can emit exactly one blank-line separator between two
sections that both printed something — never a leading separator before
the first section, and never a stray blank line when a section had
nothing to report.
Appends "{count} {label}" (styled with color) to parts when count
is nonzero. Collapses the repeated if count > 0 { parts.push(color(...)) } idiom used when building summary footers from several counters.