feat(enrich): add metadata enrichment queue UI

Home page shows "Needs metadata" card when incomplete documents exist.
/enrich list shows all incomplete documents; /enrich/[id] provides a
split PDF-preview + compact form view with Skip / Save / Save & reviewed
actions that auto-advance through the queue.

New document page gets Save vs Save & reviewed split. Edit page gets
"Mark for review" secondary button to push a document back into the queue.

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

frontend/messages/es.json

@@ -274,5 +274,21 @@
 	"upload_duplicate": "{filename} ya existe —",
 	"upload_duplicate_link": "Ver documento",
 	"upload_invalid_type": "{filename}: formato de archivo no admitido",
-	"upload_error": "Error al subir {filename}"
+	"upload_error": "Error al subir {filename}",
+	"enrich_list_back": "Volver a la vista general",
+	"enrich_list_count": "documentos",
+	"btn_save_and_mark_reviewed": "Guardar y marcar como revisado",
+	"btn_mark_for_review": "Marcar para revisión",
+	"enrich_needs_metadata_title": "Documentos sin metadatos",
+	"enrich_needs_metadata_count": "{count} documento(s) esperando metadatos",
+	"enrich_needs_metadata_cta": "Completar ahora",
+	"enrich_list_heading": "Documentos sin metadatos",
+	"enrich_list_empty_heading": "Todos los documentos completos",
+	"enrich_list_empty_body": "No hay documentos que necesiten metadatos.",
+	"enrich_list_start": "Comenzar revisión",
+	"enrich_progress": "{count} restante(s)",
+	"enrich_skip": "Omitir",
+	"enrich_done_heading": "¡Todo listo!",
+	"enrich_done_body": "Todos los documentos han sido procesados.",
+	"enrich_back_to_list": "Volver a la lista"
 }