Name a deleted target on its historical deliveries (closes #211)

Deleting a target soft deletes its row while its deliveries survive
in the per-webhook database, so the event log kept rendering the
history and lost the label: every historical row read ": delivered"
and the deliveries block was headed by an empty name.

loadTargetMap already loaded soft-deleted rows Unscoped for the
redactor half, then discarded them before building the view half.
It now builds both halves from every loaded row, and TargetView
carries a Deleted flag with a DisplayName that renders
"name (deleted)" — an operator debugging an old delivery needs to
know the target is gone, not just what it was called.

The views still come from NewTargetViews, so a deleted target's
configuration is masked by exactly the code that masks a live
one's. The widening is confined to this map, which feeds only
DeliveryView.Target on the event log page: the source detail
target list, the target edit form, the receiver and resubmit fan-out
and the delivery engine each resolve targets through their own
scoped queries, and the replay path keeps refusing a deleted target.

internal/handlers/source_management.go

@@ -860,11 +860,16 @@ func (h *Handlers) HandleSourceLogs() http.HandlerFunc {
 //
 // The load is Unscoped because deleting a target only soft
 // deletes the row while its deliveries survive in the
-// per-webhook database: a scoped load leaves those deliveries
-// with a zero redactor, which renders their response bodies
-// unredacted. Only the redactor half of the map is built from
-// deleted rows. The view half, which is what the page lists,
-// stays scoped.
+// per-webhook database. Both halves of the map need those rows:
+// a scoped load leaves an old delivery with a zero redactor,
+// which renders its response bodies unredacted, and with a zero
+// view, which renders its target as a blank name.
+//
+// This map is historical display only. It is built for the event
+// log page and reaches nothing but DeliveryView.Target: the
+// target list on the source detail page, the edit form and the
+// replay path each resolve targets themselves, and a deleted row
+// is refused there as before.
 func (h *Handlers) loadTargetMap(
 	webhookID string,
 ) (map[string]eventLogTarget, error) {
@@ -880,21 +885,18 @@ func (h *Handlers) loadTargetMap(
 	targetMap := make(
 		map[string]eventLogTarget, len(targets),
 	)
-	live := make([]database.Target, 0, len(targets))
 
 	for i := range targets {
 		targetMap[targets[i].ID] = eventLogTarget{
 			Redactor: delivery.NewRedactor(&targets[i]),
 		}
-
-		if !targets[i].DeletedAt.Valid {
-			live = append(live, targets[i])
-		}
 	}
 
 	// The views come from NewTargetViews rather than being
-	// rebuilt here, so the masking rules stay in one place.
-	for _, v := range delivery.NewTargetViews(live) {
+	// rebuilt here, so the masking rules stay in one place and a
+	// deleted target's configuration is masked by the same code
+	// that masks a live one's.
+	for _, v := range delivery.NewTargetViews(targets) {
 		entry := targetMap[v.ID]
 		entry.View = v
 		targetMap[v.ID] = entry