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).",