freq dropdown now spawns 第1次..第6次 window selectors (凌晨批次/上午/
下午/晚间), each run placed independently — e.g. reuters-world 2×/day as
overnight+afternoon → 02:00 + 12:00. Sources without explicit windows keep
auto semantics (first run in the deadline batch + extras evenly across
day_window); legacy string windows normalized. JS toggles run selectors
with the freq value; intent persists as a runs list in schedule-plan.json.