compaction-counter: expose count/auto/manual/unknown/reclaimed as selectable raw values for composition #450

compaction-counter renders count + trigger split + reclaimed as one fixed string (N (n auto, n manual) <arrow>X). To let a statusline compose its own layout (own icons/separators between parts, like the token widgets do), add a metadata selector for which sub-metric the widget outputs — e.g. metric: count|auto|manual|unknown|reclaimed — emitting that single number in rawValue mode.

Users could then concatenate several instances with custom-symbol labels/separators instead of the built-in format. The current combined output stays the default.