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.

templates/source_logs.html

@@ -39,7 +39,7 @@
                     <div class="flex items-center gap-4">
                         {{range .Deliveries}}
                         <span class="text-xs {{if eq .Status "delivered"}}text-green-600{{else if eq .Status "failed"}}text-red-600{{else if eq .Status "retrying"}}text-yellow-600{{else}}text-gray-400{{end}}">
-                            {{.Target.Name}}: {{.Status}}
+                            {{.Target.DisplayName}}: {{.Status}}
                         </span>
                         {{end}}
                         <span class="text-xs text-gray-400">{{.CreatedAt.Format "2006-01-02 15:04:05"}}</span>
@@ -74,7 +74,7 @@
                             <div class="py-2" x-data="{ attempts: false }">
                                 <div class="flex items-center justify-between cursor-pointer" @click="attempts = !attempts">
                                     <div class="flex items-center gap-3">
-                                        <span class="text-sm text-gray-700">{{.Target.Name}}</span>
+                                        <span class="text-sm text-gray-700">{{.Target.DisplayName}}</span>
                                         <span class="text-xs {{if eq .Status "delivered"}}text-green-600{{else if eq .Status "failed"}}text-red-600{{else if eq .Status "retrying"}}text-yellow-600{{else}}text-gray-400{{end}}">{{.Status}}</span>
                                     </div>
                                     <div class="flex items-center gap-3">