M1: key management, backup locations and occ commands

- migration: ngb_targets, ngb_runs, ngb_snapshots
- KeyService: master key stored encrypted with the instance secret
  (unattended backups), passphrase-wrapped copy in every repository and
  in the recovery kit, recorded admin confirmation per key fingerprint
- TargetService: locations built from files_external backends without a
  mount; files_external is loaded through IAppManager::loadApp() and its
  enabled state is left alone; credentials encrypted with ICrypto;
  existing repositories are adopted only if made with this key, and a
  repository cannot be registered twice
- Repository: initWithKey/openWithKey with an encrypted key check
- occ: backup:key:init|kit|confirm, backup:target:backends|add|list|remove

lib/Command/KeyKit.php

@@ -0,0 +1,48 @@
+<?php
+
+declare(strict_types=1);
+
+// SPDX-FileCopyrightText: 2026 Dillard Blom
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+namespace OCA\NgBackup\Command;
+
+use OCA\NgBackup\Service\KeyService;
+use Symfony\Component\Console\Command\Command;
+use Symfony\Component\Console\Input\InputInterface;
+use Symfony\Component\Console\Input\InputOption;
+use Symfony\Component\Console\Output\OutputInterface;
+
+class KeyKit extends Command {
+	public function __construct(
+		private KeyService $keys,
+	) {
+		parent::__construct();
+	}
+
+	protected function configure(): void {
+		$this->setName('backup:key:kit')
+			->setDescription('Write the recovery kit (passphrase-protected key) to a file or stdout')
+			->addOption('output', 'o', InputOption::VALUE_REQUIRED, 'File to write (default: stdout)');
+	}
+
+	protected function execute(InputInterface $input, OutputInterface $output): int {
+		if (!$this->keys->isInitialized()) {
+			$output->writeln('<error>No backup key yet: run occ backup:key:init first.</error>');
+			return 1;
+		}
+		$json = json_encode($this->keys->recoveryKit(), JSON_PRETTY_PRINT | JSON_UNESCAPED_SLASHES | JSON_THROW_ON_ERROR) . "\n";
+		$file = $input->getOption('output');
+		if ($file === null) {
+			$output->write($json, false, OutputInterface::OUTPUT_RAW);
+			return 0;
+		}
+		if (file_put_contents($file, $json) === false) {
+			$output->writeln("<error>Cannot write $file</error>");
+			return 1;
+		}
+		@chmod($file, 0600);
+		$output->writeln("Recovery kit written to <info>$file</info>. Copy it off this server, then run <info>occ backup:key:confirm</info>.");
+		return 0;
+	}
+}