Event log: show attempt and delivery times, label replays, zone event times (closes #386)

Each attempt shows when it was recorded and each delivery when it was
created, in the event log and on the event's page. The event log's
event times read as the recent events list does: how long ago, with
the full UTC time on hover.

A delivery records whether Replay created it, in a new replay column
added to the delivery model in place. Such a delivery is labelled a
replay in the event's summary line and in both pages' delivery lists.

Model: opus-5-5

internal/handlers/target_list.go

@@ -88,8 +88,7 @@ func (h *Handlers) deliveryPausedView(
 }
 
 // newPausedView is a PausedView of deliveries paused until the given
-// time. A time not on the current UTC day is written with its date, as
-// the event log writes its times.
+// time. A time not on the current UTC day is written with its date.
 func newPausedView(until time.Time) *PausedView {
 	until = until.UTC()