Restore missing document-generator files

Restores index.ts (component exports) and page.tsx (793 lines)
for the SDK document generator module.

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

admin-v2/app/(sdk)/sdk/document-generator/components/index.ts

@@ -0,0 +1,9 @@
+/**
+ * Document Generator Components
+ *
+ * Diese Komponenten integrieren die Einwilligungen-Datenpunkte
+ * in den Dokumentengenerator.
+ */
+
+export { DataPointsPreview } from './DataPointsPreview'
+export { DocumentValidation } from './DocumentValidation'