Polls Radicale for today's events, writes calendar_busy and calendar_event
facts through CoreAPI. Only writes on value change (same append-only
discipline as mavpoll).
Usage: mavcaldav -socket <core> -url <radicale> -user <u> -pass <p>
Flags: -interval (default 5m), -timeout (default 10s).
Fires immediately on start, then on interval.
iCal parser supports UTC and local DTSTART/DTEND, skips all-day events.
kami