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

In the event log and on an event's page, attempts and deliveries showed no time, event times had no zone, and a replay looked like the original it repeated. Each attempt now shows when its result was recorded and each delivery when it was created, as how long ago with the full UTC time on hover, and the event log's event times read the same way. A delivery created by Replay records it in a new `replay` column and is labelled a replay in the event's summary line and its delivery list; replays made before this change are not labelled. A delivery's row is now drawn by one template, `delivery_row`, that both pages share.

Model: opus-5-5

internal/database/model_delivery.go

@@ -56,6 +56,10 @@ type Delivery struct {
 	// the index.
 	FinishedAt *time.Time `gorm:"index:idx_deliveries_status,priority:3" json:"finishedAt,omitempty"`
 
+	// Replay is set on a delivery created by the event log's Replay
+	// action, so the pages can tell it from the delivery it repeats.
+	Replay bool `gorm:"not null;default:false" json:"replay"`
+
 	// Relations. No model marshals the record it belongs to:
 	// Event.Deliveries and Target.Deliveries lead back here, and the
 	// JSON could loop.