Rename category_self_mute_clear_marker_ts (scalar) to category_self_mute_clear_markers (dict[str, int]). The lode-3 settings UI needs to clear self-mute per category, not globally. No back-compat shim — lode 1 just shipped and there are no users to migrate. Adds compute_category_mute_state() helper so policy and the new settings API share one source of truth for mute state.