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.
Both pages draw a delivery's row from one shared template.

Model: opus-5-5

templates/delivery_attempts.html

@@ -9,6 +9,7 @@
 <div class="rounded-md bg-white border border-gray-200 p-2">
     <div class="flex flex-wrap items-center gap-3 text-xs">
         <span class="text-gray-500">Attempt {{.AttemptNum}}</span>
+        <span class="text-gray-500" title="{{.RanUTC}}">{{.Ran}}</span>
         <span class="{{if .Success}}text-green-600{{else}}text-red-600{{end}}">{{if not .Success}}failure{{else if eq $.Target.Type "database"}}archived{{else if eq $.Target.Type "log"}}written to the log{{else}}success{{end}}</span>
         {{/* A database or log target sends no HTTP request, so its attempts have no status code. */}}
         {{if not (eq $.Target.Type "database" "log")}}