Run batches and import JSON or CSV through the API

Each operation is dispatched as a request of its own, so a batch is held to
the same validation and permissions as the calls it contains.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

app/Support/Batch/BatchAborted.php

@@ -0,0 +1,12 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Support\Batch;
+
+use RuntimeException;
+
+/**
+ * Thrown inside the batch's transaction to undo it.
+ */
+final class BatchAborted extends RuntimeException {}