feat(customers): show vehicles and delete customer

- get_customer now returns fleet_vehicles assigned to the customer.

- Added DELETE /pos/api/customers/<id> soft-delete (is_active=false) with customers.delete permission.

- Added Vehicles section in customer detail panel.

- Added Eliminar button in quick actions (owner/admin/customers.delete).

pos/static/css/customers.css

@@ -1209,6 +1209,16 @@
       color: #000;
     }
 
+    .action-btn--danger {
+      color: var(--color-error);
+      border-color: var(--color-error);
+    }
+
+    .action-btn--danger:hover {
+      background-color: var(--color-error);
+      color: #fff;
+    }
+
     .action-btn__icon {
       width: 20px;
       height: 20px;