R1:00a1dec7a6dc

Render timezones in event reminder mail, and render them more nicely

Summary:
Fixes T12356.

- In this mail, we currently render "6:00 AM". Instead, render "6:00 AM (PDT)" or similar. This is consistent with times in other modern Transaction mail.
- Previously, we would render "UTC-7". Render "PDT" instead. For obscure zones with no known timezone abbreviation, fall back to "UTC-7".

Test Plan:
- Used `bin/calendar notify --minutes X` to trigger notifications, read email bodies.
- Used this script…