M5: deletion delay with trash, passphrase slots, ransomware documentation

- removed snapshots go to a trash on the location and their data is only
  freed after the deletion delay, which is chosen when the key is created
  (default 7 days, 1-365) and cannot be changed afterwards; any admin can
  bring them back (occ backup:trash, backup:trash:restore, web UI)
- up to three passphrase slots open the same master key (like LUKS), so
  one person leaving or dying does not lock the company out; slot changes
  are written to every location, announced to all admins and require a
  new recovery kit confirmation, while backups keep running
- occ backup:key:slots, backup:key:slot:add|replace|remove; key init takes
  --label and --delete-delay-days
- web UI: deletion delay and first slot at key creation, slot management,
  trash per location with restore; all behind password confirmation
- README: key, slots (safe / CTO / head of IT), and protection against
  ransomware: object lock in compliance mode (e.g. 90 days), credentials
  without delete rights, provider snapshots, off-site copy

lib/Crypto/KeyRing.php

@@ -76,6 +76,23 @@ final class KeyRing {
 		];
 	}
 
+	/**
+	 * Open a key field that is either one wrapped key or {"slots": [{slot, label, key}, ...]}:
+	 * every slot holds the same master key under its own passphrase.
+	 */
+	public static function unwrapAny(array $field, #[\SensitiveParameter] string $passphrase): self {
+		if (!isset($field['slots'])) {
+			return self::unwrap($field, $passphrase);
+		}
+		foreach ($field['slots'] as $slot) {
+			try {
+				return self::unwrap($slot['key'], $passphrase);
+			} catch (CryptoException) {
+			}
+		}
+		throw new CryptoException('Wrong passphrase or damaged key');
+	}
+
 	/** @param array{v:int, salt:string, ops:int, mem:int, nonce:string, key:string} $wrapped */
 	public static function unwrap(array $wrapped, #[\SensitiveParameter] string $passphrase): self {
 		$b64 = static fn (string $s): string => sodium_base642bin($s, SODIUM_BASE64_VARIANT_ORIGINAL);