Start a turn when a schedule comes due

The daemon runs the schedules next to WhatsApp. At its time, a schedule
goes to the chat as a work message that starts with [Schedule ID] and
starts a turn of the root agent, which does the task or spawns a
subagent for long work. The message ends with the empty reply line, so a
task that finds nothing for the user gives no message.

The runner waits until the first due time, at most one minute at a time,
so it sees a suspend of the machine or a change of the clock within a
minute. A set or a remove wakes it. It logs all due schedules in due
order, flushes the log, ends each run in the file, and wakes the turn
loop once, as the WhatsApp batches do. A crash between the flush and the
file write makes a run repeat once. So a schedule that came due while
the daemon was stopped runs once at the next start, with the line that
the run is late.

Telegram does not send the work message, because the reply of the agent
carries its content. The terminal client shows it. The README describes
the schedules, the cron subset, the limit of 5 minutes, and the rules
for daylight saving time.

Issue: 60e4e4f