Offer no Replay for a delivery to a deleted target (closes #387)

The event log offered Replay on a delivery whose target was deleted,
and the refusal told the operator to recreate the target and replay.
That cannot work: a recreated target is a new one the old delivery
does not name, so the replay is refused again. The Replay button is
now left off such a delivery, whose row already names the target as
deleted, and the refusal a page left open can still reach now points
to Resubmit, which sends the event to the webhook's currently active
targets.

Model: opus-5-5

internal/handlers/delivery_replay_test.go

@@ -513,7 +513,11 @@ func TestHandleSourceLogs_RendersReplayControlAndBanner(t *testing.T) {
 	)
 
 	assert.Contains(t, refused, "alert-error")
-	assert.Contains(t, refused, "has been deleted")
+	assert.Contains(
+		t, refused,
+		"has been deleted. Use Resubmit to send the event "+
+			"to the webhook",
+	)
 
 	// An outcome code nobody issued renders no banner at all.
 	unknown := renderSourceLogsPageWithQuery(