feat: add LDAP authentication as per-tenant login method

Add LDAP as a third authentication option alongside local password and
Microsoft Entra ID SSO. Per-tenant configuration supports Active Directory,
OpenLDAP, and FreeIPA with configurable attribute mapping, search-then-bind
and direct-bind methods, encrypted bind credentials (AES-256-GCM),
profile sync on login, and user auto-provisioning via external identity
linking.

Includes admin UI for connection settings with test-connection button,
login page LDAP form, 25 new PHPUnit tests, and de/en translations.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

lib/Service/Auth/LdapConnectionGateway.php

@@ -0,0 +1,67 @@
+<?php
+
+namespace MintyPHP\Service\Auth;
+
+/**
+ * Thin wrapper around PHP ldap_* functions for testability.
+ *
+ * Every public method maps 1:1 to a native ldap_* call.
+ * In tests, this gateway is replaced with a mock.
+ */
+class LdapConnectionGateway
+{
+    /** @return \LDAP\Connection|false */
+    public function connect(string $uri): \LDAP\Connection|false
+    {
+        return ldap_connect($uri);
+    }
+
+    public function setOption(\LDAP\Connection $conn, int $option, mixed $value): bool
+    {
+        return ldap_set_option($conn, $option, $value);
+    }
+
+    public function startTls(\LDAP\Connection $conn): bool
+    {
+        return ldap_start_tls($conn);
+    }
+
+    public function bind(\LDAP\Connection $conn, ?string $dn = null, ?string $password = null): bool
+    {
+        return @ldap_bind($conn, $dn, $password);
+    }
+
+    /** @return \LDAP\Result|false */
+    public function search(\LDAP\Connection $conn, string $baseDn, string $filter, array $attributes = [], int $scope = 0): \LDAP\Result|false
+    {
+        if ($scope === 1) {
+            return @ldap_list($conn, $baseDn, $filter, $attributes);
+        }
+        return @ldap_search($conn, $baseDn, $filter, $attributes);
+    }
+
+    public function getEntries(\LDAP\Connection $conn, \LDAP\Result $result): array|false
+    {
+        return ldap_get_entries($conn, $result);
+    }
+
+    public function escape(string $value, string $ignore = '', int $flags = 0): string
+    {
+        return ldap_escape($value, $ignore, $flags);
+    }
+
+    public function errno(\LDAP\Connection $conn): int
+    {
+        return ldap_errno($conn);
+    }
+
+    public function error(\LDAP\Connection $conn): string
+    {
+        return ldap_error($conn);
+    }
+
+    public function unbind(\LDAP\Connection $conn): bool
+    {
+        return @ldap_unbind($conn);
+    }
+}