Fix edge gateway relay binding reactivation

Reactivate existing relay binding rows when a gateway/relay pair is re-added after soft deletion, avoiding duplicate uniq_edge_gateway_binding inserts. Add regression coverage for the reactivation path.

services/nginx/app/modules/edgegateway/classes/edge_gateway_manager.php

@@ -799,7 +799,6 @@ class edge_gateway_manager
             $existing = (new edge_gateway_relay_bindings_o())->getFieldsWhere([
                 'gateway_id' => $gatewayId,
                 'relay_id' => $relayId,
-                'deleted_at' => null,
             ], ['id']);
 
             if ($existing !== []) {
@@ -818,6 +817,7 @@ class edge_gateway_manager
                 $bindingObject->approved_by->set($userId);
                 $bindingObject->approved_at->set($this->now());
                 $bindingObject->metadata_json->set($bindingMetadata);
+                $bindingObject->deleted_at->set(null);
                 continue;
             }