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>

web/css/components/app-flash.css

@@ -1,3 +1,4 @@
+@layer components {
 .notice {
     --app-notice-border-color: var(--app-muted-border-color);
     --app-notice-background-color: var(--app-card-background-color);
@@ -127,4 +128,5 @@
 
 .notice li {
     list-style: none;
-}
+}
+}