Give the root agent the schedule tools

The root agent gets three tools. schedule_set adds a schedule with a
task text and either a local time or a cron expression, and answers with
its ID and next time. schedule_list gives each schedule with its ID,
next time, cron expression or once, and text. schedule_remove removes
one by its ID.

The descriptions tell the agent to set a schedule only when the user
asks, to write the text as an order to itself, and to turn a time such
as "tomorrow at 9" into a local time from the Now line. The cron
description gives the limit of 5 minutes between runs. The prompt text
does not change, so it stays near the reference design.

The daemon opens agent/schedules.json at its start. The toolbox of a
subagent has no schedules, so the tools are unknown there, as the
WhatsApp tools are. Compactions send the new tools too, so they keep the
shared prompt cache.

Issue: 60e4e4f