1.0.1: label for "Back up now", retention explained in the trash, occ times in the schedule's zone, single-file restore to a directory, leftovers of a stopped restore removed

- Admin page: an optional label (at most 100 characters) for a backup started with "Back up now";
  an (i) by "removed by retention policy" in the trash that explains what it means and until when
  the restore point can be brought back. backup:trash says the same below its list.
- backup:status, backup:list, backup:trash and backup:browse show times in the zone of the daily
  schedule and name it, instead of the server's UTC.
- backup:restore --to-directory of a file restored nothing: the path got a "/" appended.
- A restore removes "<name>.ngb-restore-<hex>" temporaries that a stopped restore left in the
  folders it writes to.
- Roadmap: the cron warning (#13), reading ahead from S3/SMB and --salvage move to 1.0.2.

lib/Service/BackupService.php

@@ -34,6 +34,8 @@ use Psr\Log\LoggerInterface;
  */
 final class BackupService {
 	public const KIND_FULL = 'full';
+	/** Characters of a snapshot label (the column holds 255) */
+	public const LABEL_MAX = 100;
 
 	/** @var \WeakMap<Repository, string> the location settings each kept repository was opened with */
 	private \WeakMap $openedWith;
@@ -57,6 +59,10 @@ final class BackupService {
 	}
 
 	public function start(Target $target, string $label = ''): Run {
+		$label = trim($label);
+		if (mb_strlen($label) > self::LABEL_MAX) {
+			throw new \InvalidArgumentException('A label has at most ' . self::LABEL_MAX . ' characters');
+		}
 		if (!$this->keys->everConfirmed()) {
 			throw new \RuntimeException('Confirm the recovery kit first (occ backup:key:confirm)');
 		}