M2: full backup runs (database, config, data) with occ and cron

BackupService starts a run per location (database dump in one
transaction, then config + data directory as a resumable file run),
stores the state in ngb_runs after every step, locks a run while a step
executes and records the snapshot. Previews, logs, updater backups and
per-user cache/uploads are excluded (TreeWalker now supports patterns).
BackupJob (every 5 min) starts the daily schedule and steps running runs
with a short budget under web cron and a long one under system cron.
occ: backup:run, backup:status, backup:list.

Tested on NC34/PostgreSQL: first run 128 files / 1 GiB in 64 s (443 MiB
uploaded to S3), unchanged second run 2 s / 0 bytes; a background run to
SFTP completed through cron.php.

lib/Db/Snapshot.php

@@ -0,0 +1,43 @@
+<?php
+
+declare(strict_types=1);
+
+// SPDX-FileCopyrightText: 2026 Dillard Blom
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+namespace OCA\NgBackup\Db;
+
+use OCP\AppFramework\Db\Entity;
+
+/**
+ * @method int getTargetId()
+ * @method void setTargetId(int $v)
+ * @method string getSnapshotId()
+ * @method void setSnapshotId(string $v)
+ * @method string getKind()
+ * @method void setKind(string $v)
+ * @method string|null getLabel()
+ * @method void setLabel(?string $v)
+ * @method int getCreatedAt()
+ * @method void setCreatedAt(int $v)
+ * @method int|null getFiles()
+ * @method void setFiles(?int $v)
+ * @method int|null getBytes()
+ * @method void setBytes(?int $v)
+ */
+class Snapshot extends Entity {
+	protected int $targetId = 0;
+	protected string $snapshotId = '';
+	protected string $kind = '';
+	protected ?string $label = null;
+	protected int $createdAt = 0;
+	protected ?int $files = null;
+	protected ?int $bytes = null;
+
+	public function __construct() {
+		$this->addType('targetId', 'integer');
+		$this->addType('createdAt', 'integer');
+		$this->addType('files', 'integer');
+		$this->addType('bytes', 'integer');
+	}
+}