feat(frontend): add confirmation dialog before deleting users, peers, and interfaces (#652)

Add a browser confirm() dialog to the delete functions in UserEditModal,
PeerEditModal, and InterfaceEditModal to prevent accidental deletions.
The bulk-delete actions in UserView already had this protection; this
change brings single-item deletion in line with that behavior.

Translation keys (confirm-delete) added for all 10 supported locales:
de, en, es, fr, ko, pt, ru, uk, vi, zh.

Signed-off-by: LeC-D <leo.openc@gmail.com>

frontend/src/lang/translations/es.json

@@ -366,6 +366,8 @@
       "admin": {
         "label": "Es administrador"
       }
+    },
+      "confirm-delete": "Seguro que desea eliminar el usuario '{id}'?"
     },
     "interface-view": {
       "headline": "Configuración de la interfaz:"
@@ -493,7 +495,8 @@
           "placeholder": "Keepalive Persistente (0 = por defecto)"
         }
       },
-      "button-apply-defaults": "Aplicar Valores Predeterminados de peers"
+      "button-apply-defaults": "Aplicar Valores Predeterminados de peers",
+      "confirm-delete": "Seguro que desea eliminar la interfaz '{id}'?"
     },
     "peer-view": {
       "headline-peer": "Peer:",
@@ -613,7 +616,8 @@
       },
       "expires-at": {
         "label": "Fecha de expiración"
-      }
+      },
+      "confirm-delete": "Seguro que desea eliminar el par '{id}'?"
     },
     "peer-multi-create": {
       "headline-peer": "Crear múltiples peers",