feat(admin): surface skipped file count in ImportStatusCard

Adds SkippedFile to the local ImportStatus type and updates
ImportStatusCard to show an amber skipped-count section with a
collapsible filename list in the DONE state. Only rendered when
skipped > 0. i18n keys added for de/en/es.

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

frontend/messages/de.json

@@ -350,6 +350,7 @@
 	"admin_system_import_status_running": "Import läuft…",
 	"admin_system_import_status_done": "Import abgeschlossen",
 	"admin_system_import_status_done_label": "Dokumente verarbeitet",
+	"admin_system_import_skipped_label": "übersprungen",
 	"admin_system_import_status_failed": "Import fehlgeschlagen",
 	"admin_system_import_failed_no_spreadsheet": "Keine Tabellendatei gefunden.",
 	"admin_system_import_failed_internal": "Interner Fehler beim Import.",

frontend/messages/en.json

@@ -350,6 +350,7 @@
 	"admin_system_import_status_running": "Import running…",
 	"admin_system_import_status_done": "Import complete",
 	"admin_system_import_status_done_label": "Documents processed",
+	"admin_system_import_skipped_label": "skipped",
 	"admin_system_import_status_failed": "Import failed",
 	"admin_system_import_failed_no_spreadsheet": "No spreadsheet file found.",
 	"admin_system_import_failed_internal": "Import failed due to an internal error.",

frontend/messages/es.json

@@ -350,6 +350,7 @@
 	"admin_system_import_status_running": "Importación en curso…",
 	"admin_system_import_status_done": "Importación completada",
 	"admin_system_import_status_done_label": "Documentos procesados",
+	"admin_system_import_skipped_label": "omitidos",
 	"admin_system_import_status_failed": "Importación fallida",
 	"admin_system_import_failed_no_spreadsheet": "No se encontró ninguna hoja de cálculo.",
 	"admin_system_import_failed_internal": "Error interno durante la importación.",