The briefing was formatting event start_dt directly in UTC instead of
converting to the user's local timezone. Also, the day_start/day_end
query window was naive (UTC), so events at the edges of the user's day
could be missed or included incorrectly.
Now reads user_timezone setting, uses it for today's date boundary and
for converting each event's start_dt before formatting.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>