feat(admin): add document preview functionality to adult verification

- Implemented a preview section for adult verification documents, allowing users to view images and PDFs inline.
- Added localization support for preview titles and messages in German, English, and Spanish.
- Enhanced the component's state management to handle preview visibility and cleanup.

frontend/src/i18n/locales/de/admin.json

@@ -42,6 +42,9 @@
             "reject": "Ablehnen",
             "resetPending": "Auf Prüfung setzen",
             "openDocument": "Dokument ansehen",
+            "previewTitle": "Nachweis-Vorschau",
+            "closePreview": "Vorschau schließen",
+            "previewUnavailable": "Für diesen Dateityp ist hier keine Vorschau verfügbar.",
             "empty": "Keine passenden Anfragen gefunden.",
             "loadError": "Die Freigaben konnten nicht geladen werden.",
             "updateError": "Der Status konnte nicht geändert werden.",

frontend/src/i18n/locales/en/admin.json

@@ -42,6 +42,9 @@
             "reject": "Reject",
             "resetPending": "Set pending",
             "openDocument": "Open document",
+            "previewTitle": "Proof preview",
+            "closePreview": "Close preview",
+            "previewUnavailable": "No inline preview is available for this file type.",
             "empty": "No matching requests found.",
             "loadError": "Could not load approvals.",
             "updateError": "Could not update the status.",

frontend/src/i18n/locales/es/admin.json

@@ -42,6 +42,9 @@
             "reject": "Rechazar",
             "resetPending": "Poner en revisión",
             "openDocument": "Abrir documento",
+            "previewTitle": "Vista previa de la prueba",
+            "closePreview": "Cerrar vista previa",
+            "previewUnavailable": "No hay vista previa integrada para este tipo de archivo.",
             "empty": "No se han encontrado solicitudes.",
             "loadError": "No se pudieron cargar las aprobaciones.",
             "updateError": "No se pudo actualizar el estado.",