add composer-unused, comprehensive docs, and project restructure

- Add icanhazstring/composer-unused as dev dependency for dependency hygiene checks
- Add German documentation (docs/) covering architecture, conventions, workflows, and developer checklists
- Add API layer (ApiAuth, ApiBootstrap, ApiResponse), audit, scheduler, custom fields, and SSO services
- Add Microsoft OIDC SSO, API token management, and user lifecycle features
- Add swagger-ui vendor integration and OpenAPI spec
- Add production Docker setup and bin/ scripts
- Update composer dependencies, config, templates, and frontend assets throughout

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/Repository/User/UserExternalIdentityRepository.php

@@ -0,0 +1,55 @@
+<?php
+
+namespace MintyPHP\Repository\User;
+
+use MintyPHP\DB;
+
+class UserExternalIdentityRepository
+{
+    private static function unwrap($row): ?array
+    {
+        if (!$row || !is_array($row)) {
+            return null;
+        }
+        if (isset($row['user_external_identities']) && is_array($row['user_external_identities'])) {
+            return $row['user_external_identities'];
+        }
+        return $row;
+    }
+
+    public static function findByProviderTidOid(string $provider, string $tid, string $oid): ?array
+    {
+        $row = DB::selectOne(
+            'select id, user_id, provider, oid, tid, issuer, subject, email_at_link_time, created from user_external_identities where provider = ? and tid = ? and oid = ? limit 1',
+            $provider,
+            $tid,
+            $oid
+        );
+        return self::unwrap($row);
+    }
+
+    public static function findByProviderIssuerSubject(string $provider, string $issuer, string $subject): ?array
+    {
+        $row = DB::selectOne(
+            'select id, user_id, provider, oid, tid, issuer, subject, email_at_link_time, created from user_external_identities where provider = ? and issuer = ? and subject = ? limit 1',
+            $provider,
+            $issuer,
+            $subject
+        );
+        return self::unwrap($row);
+    }
+
+    public static function createLink(array $data)
+    {
+        return DB::insert(
+            'insert into user_external_identities (user_id, provider, oid, tid, issuer, subject, email_at_link_time, created) values (?,?,?,?,?,?,?,NOW())',
+            (string) ((int) ($data['user_id'] ?? 0)),
+            (string) ($data['provider'] ?? ''),
+            (string) ($data['oid'] ?? ''),
+            (string) ($data['tid'] ?? ''),
+            (string) ($data['issuer'] ?? ''),
+            (string) ($data['subject'] ?? ''),
+            $data['email_at_link_time'] ?? null
+        );
+    }
+}