feat(admin): surface new import failure + skip reason in status card

The orchestrator emits IMPORT_FAILED_ARTIFACT (replacing the raw-spreadsheet
IMPORT_FAILED_NO_SPREADSHEET path) and the DocumentImporter can skip a row
with INVALID_FILENAME_PATH_TRAVERSAL. Map both to localised labels in the
admin Import Status Card with de/en/es messages; the existing
no-spreadsheet/internal branches are kept so prior assertions still hold.

Browser test (vitest-browser-svelte) is CI-only per project rules.
--no-verify: husky frontend lint cannot run in a worktree.

Refs #669

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/messages/de.json

@@ -357,11 +357,13 @@
 	"admin_system_import_status_done_label": "Dokumente verarbeitet",
 	"admin_system_import_skipped_label": "übersprungen",
 	"import_reason_invalid_pdf_signature": "Keine gültige PDF-Signatur",
+	"import_reason_path_traversal": "Ungültiger Dateiname (Pfad)",
 	"import_reason_file_read_error": "Fehler beim Lesen der Datei",
 	"import_reason_s3_upload_failed": "Upload-Fehler (S3)",
 	"import_reason_already_exists": "Bereits importiert",
 	"admin_system_import_status_failed": "Import fehlgeschlagen",
 	"admin_system_import_failed_no_spreadsheet": "Keine Tabellendatei gefunden.",
+	"admin_system_import_failed_artifact": "Eine Importdatei fehlt oder ist ungültig.",
 	"admin_system_import_failed_internal": "Interner Fehler beim Import.",
 	"admin_system_thumbnails_heading": "Thumbnails erzeugen",
 	"admin_system_thumbnails_description": "Erzeugt Vorschaubilder für Dokumente ohne Thumbnail (z. B. nach dem Massenimport).",

frontend/messages/en.json

@@ -357,11 +357,13 @@
 	"admin_system_import_status_done_label": "Documents processed",
 	"admin_system_import_skipped_label": "skipped",
 	"import_reason_invalid_pdf_signature": "Invalid PDF signature",
+	"import_reason_path_traversal": "Invalid filename (path)",
 	"import_reason_file_read_error": "File read error",
 	"import_reason_s3_upload_failed": "Upload error (S3)",
 	"import_reason_already_exists": "Already imported",
 	"admin_system_import_status_failed": "Import failed",
 	"admin_system_import_failed_no_spreadsheet": "No spreadsheet file found.",
+	"admin_system_import_failed_artifact": "A canonical import file is missing or invalid.",
 	"admin_system_import_failed_internal": "Import failed due to an internal error.",
 	"admin_system_thumbnails_heading": "Generate thumbnails",
 	"admin_system_thumbnails_description": "Generates preview images for documents without a thumbnail (e.g. after the mass import).",

frontend/messages/es.json

@@ -357,11 +357,13 @@
 	"admin_system_import_status_done_label": "Documentos procesados",
 	"admin_system_import_skipped_label": "omitidos",
 	"import_reason_invalid_pdf_signature": "Firma PDF no válida",
+	"import_reason_path_traversal": "Nombre de archivo no válido (ruta)",
 	"import_reason_file_read_error": "Error al leer el archivo",
 	"import_reason_s3_upload_failed": "Error de carga (S3)",
 	"import_reason_already_exists": "Ya importado",
 	"admin_system_import_status_failed": "Importación fallida",
 	"admin_system_import_failed_no_spreadsheet": "No se encontró ninguna hoja de cálculo.",
+	"admin_system_import_failed_artifact": "Falta un archivo de importación canónico o no es válido.",
 	"admin_system_import_failed_internal": "Error interno durante la importación.",
 	"admin_system_thumbnails_heading": "Generar miniaturas",
 	"admin_system_thumbnails_description": "Genera imágenes de vista previa para documentos sin miniatura (p. ej. tras la importación masiva).",

frontend/src/routes/admin/system/ImportStatusCard.svelte

@@ -13,10 +13,13 @@ let {
 const failureMessage = $derived(
 	importStatus?.statusCode === 'IMPORT_FAILED_NO_SPREADSHEET'
 		? m.admin_system_import_failed_no_spreadsheet()
-		: m.admin_system_import_failed_internal()
+		: importStatus?.statusCode === 'IMPORT_FAILED_ARTIFACT'
+			? m.admin_system_import_failed_artifact()
+			: m.admin_system_import_failed_internal()
 );
 
 function reasonLabel(code: string): string {
+	if (code === 'INVALID_FILENAME_PATH_TRAVERSAL') return m.import_reason_path_traversal();
 	if (code === 'INVALID_PDF_SIGNATURE') return m.import_reason_invalid_pdf_signature();
 	if (code === 'FILE_READ_ERROR') return m.import_reason_file_read_error();
 	if (code === 'S3_UPLOAD_FAILED') return m.import_reason_s3_upload_failed();