Calendars: event dates render off-by-one / inconsistently across views (likely timezone conversion)

[mbyrdLCS]

Summary

The same recurring event renders on three different dates/days depending on which calendar view displays it. This looks like inconsistent UTC/local timezone conversion.

Test Event

• Group event 'Midweek Bible Study', created by a group leader in the member app
• Start: Wednesday, June 17, 2026, 7:00 PM (end 8:30 PM), recurring weekly, church timezone US Central (Broken Arrow, OK demo church)

Observed Renderings (2026-06-11)

1. Member app month grid (group → Events tab): event dots appear on Thursdays (June 18, 25 …) — one day late.
2. Member app day list (below the grid): clicking day 24 shows the event listed under the header 'Tuesday, June 23' — one day early relative to the clicked day, two days off from the dot.
3. Admin curated calendar (Website → Calendars → calendar detail): occurrences correctly appear on Wednesdays (June 24, July 1) — but the first occurrence (June 17) is missing entirely from the month view.

Expected

All views should show the event on Wednesdays, including the first occurrence on June 17.

Repro

1. As a group leader in the member app, create an event for a Wednesday evening (e.g. 7:00 PM local), recurring weekly.
2. Compare the member app month grid dots, the per-day list headers, and the admin curated calendar.

Environment

Chrome desktop; member app at demo0626.b1.church; admin at admin.b1.church. Event created ~2:30 PM CDT on 2026-06-11.

Side Note (UX, not a bug)

In the New Event dialog, enabling 'Recurring' defaults Frequency to Day. A missed dropdown turns a weekly Bible study into a daily event. Defaulting to 'Week' (the overwhelmingly common case) would prevent accidental daily spam.

member app month grid: the Wednesday 7 PM event's dots sitting on Thursdays

— day 18 circled/selected, but the list below is headed "Wednesday, June 17"

— admin curated calendar: correctly on Wednesdays (24th, July 1) but the June 17 first occurrence missing