Open-ended events are marked as ended the moment the start time passes

**What happens:** When an event has no end date/time (open-ended), it gets flagged as "ended" the second the start time passes. So an event scheduled to *begin* at 7pm shows as ended at 7:01pm — even though it just started. **Expected:** Open-ended events should stay in an "ongoing" / "in progress" state once the start time passes. There is no end time to compare against, so the only meaningful transition is `upcoming → ongoing`. They should never auto-flip to `ended`. **Where it shows up:** - Event detail page status badge - Event cards in list / discover views - Filter behavior ("upcoming" / "ongoing" / "ended" buckets) **Likely cause:** the lifecycle logic compares `now > end_time`, and when `end_time` is null some short-circuit defaults to "ended" (or treats null as `start_time`). The null case should fall through to "ongoing" instead. **Repro:** 1. Create an event with a start time but no end time. 2. Wait until the start time passes (or set start_time in the past). 3. Open the event — status shows as "ended" instead of "ongoing".