Add per-delivery replay to the event log (closes #203) (#240)

There was no redelivery path anywhere: once a delivery exhausted
max_retries it was failed permanently, even though the event body is
durably stored. Storing an event and being unable to re-send it defeats
the reason it is stored, and the ordinary case is a destination that was
down longer than the backoff ladder.

Adds POST /source/{sourceID}/deliveries/{deliveryID}/replay, inside the
authenticated group so it inherits MaxBodySize, CSRF, NoCache and
RequireAuth. Replay creates a NEW pending delivery against the target's
CURRENT config and hands it to the engine through the same notifier the
receiver uses, so it runs the normal path with the retry ladder, the
SSRF-guarded transport and the circuit breaker. The original delivery's
rows are never touched, and the stored event body is re-sent, never the
recorded response.

Replay is refused, with a distinct message, for a non-terminal delivery, a
deleted target, a deactivated target, and when an earlier replay of the
same event and target is still in flight. Bounded by a per-client rate
limit and by that in-flight check.

The new delivery row is written with Omit(clause.Associations) and with
neither Event nor Target populated, so it cannot upsert a targets row into
the per-webhook event database (#206).

Counted by webhooker_delivery_replays_total on the existing target_type
label. A replay also moves the ordinary attempt, outcome and duration
series, because it is a real delivery.

templates/source_logs.html

@@ -12,6 +12,10 @@
         </div>
     </div>
 
+    {{if .ReplayMessage}}
+    <div class="{{if .ReplayQueued}}alert-success{{else}}alert-error{{end}}">{{.ReplayMessage}}</div>
+    {{end}}
+
     <div class="card">
         <div class="divide-y divide-gray-100">
             {{range .Events}}
@@ -40,6 +44,23 @@
                     {{if .BodyTruncated}}
                     <p class="mt-2 text-xs text-gray-500">Body truncated for display: showing {{.BodyShownBytes}} of {{.BodyBytes}} bytes. The stored body is unchanged &mdash; <a href="/source/{{$.Webhook.ID}}/logs/{{.ID}}/body" class="text-primary-600 hover:text-primary-700 underline">download the full body</a>.</p>
                     {{end}}
+
+                    {{if .Deliveries}}
+                    <div class="mt-3 pt-4 border-t border-gray-200">
+                        {{range .Deliveries}}
+                        <div class="flex items-center justify-between py-2 text-xs text-gray-700">
+                            <span><span class="font-medium">{{.Target.Name}}</span>: {{.Status}}</span>
+                            {{if .Status.Terminal}}
+                            <form method="POST" action="/source/{{$.Webhook.ID}}/deliveries/{{.ID}}/replay" class="inline">
+                                <input type="hidden" name="csrf_token" value="{{$.CSRFToken}}">
+                                <input type="hidden" name="page" value="{{$.Page}}">
+                                <button type="submit" class="text-xs text-primary-600 hover:text-primary-700" title="Send this event to the target again">Replay</button>
+                            </form>
+                            {{end}}
+                        </div>
+                        {{end}}
+                    </div>
+                    {{end}}
                 </div>
             </div>
             {{else}}