fix(sidebar): verify folder deletion against the backend

The sidebar derives "empty folder" from the models-only list, which omits
models flagged `exclude: true`, while the delete guard walks the folder on
disk and refuses on any weight file. A folder whose models are all excluded
therefore looked empty, offered the confirmation, and then failed with
"still contains models".

The delete modal still opens on that prediction, but is now corrected by a
dry run of the very delete the user is about to confirm, so the button state
cannot contradict the backend. The confirm button stays disabled while the
check runs, and a late answer is discarded once the modal is dismissed or
retargeted. The dry run also covers weight files no scanner indexes (a lora
folder holding only a `.gguf`, say) and files that appeared after the last
scan.

`_collect_folder_manifest()` now reports `excluded_model_count`, and the
refusal names the excluded models, so the message explains the mismatch
instead of reading like a bug. Locale files carry the sync placeholders in
this commit; the translations follow.

locales/es.json

@@ -1350,6 +1350,10 @@
             "emptyNote": "Esta carpeta no contiene modelos. Los demás archivos que contenga también se eliminarán.",
             "notEmptyTitle": "La carpeta no está vacía",
             "notEmptyMessage": "Esta carpeta aún contiene modelos. Elimínalos o muévelos primero — eliminar una carpeta nunca elimina los archivos de modelo en cascada.",
+            "notEmptyMessageCount": "[TODO: Translate] This folder still contains {count} model file(s). Delete or move them first — deleting a folder never cascades over model files.",
+            "notEmptyMessageExcluded": "[TODO: Translate] This folder still contains {count} model file(s), {excluded} of them excluded from the library. Un-exclude them in Manage Excluded Models and delete them first — deleting a folder never cascades over model files.",
+            "busyTitle": "[TODO: Translate] A deletion is still pending",
+            "checking": "[TODO: Translate] Checking the folder contents...",
             "confirm": "Eliminar carpeta"
         },
         "deleteFolderResult": {
@@ -1358,6 +1362,7 @@
             "restored": "Carpeta restaurada",
             "failed": "Error al eliminar la carpeta: {message}",
             "notEmpty": "Esta carpeta aún contiene modelos. Actualiza la barra lateral e inténtalo de nuevo.",
+            "notEmptyWithCount": "[TODO: Translate] This folder still contains {count} model file(s). Refresh the sidebar and try again.",
             "busy": "Todavía hay una eliminación pendiente dentro de esta carpeta. Espera a que caduque la ventana de deshacer.",
             "unsupported": "La eliminación de carpetas no es compatible con esta página",
             "noRoot": "No hay ninguna raíz de modelo configurada"