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>

.gitignore

@@ -1,9 +1,21 @@
+# IDE
 .vscode/
+.idea/
+
+# macOS
+.DS_Store
+
+# Composer
 composer.phar
+/vendor/
+
+# Secrets / local config
 config/config.php
 .env
-/vendor/
+
+# Runtime & generated
 /web/debugger/
 /data/
 /storage/*
 !/storage/.gitkeep
+.phpunit.result.cache