Fix LoRA training Error 500 - remove Radio serialization issue

The @gradio/client was wrapping Radio component values as
{"value": "replace", "__type__": "update"} instead of plain strings,
causing the update_settings Gradio call to fail and crash the server.

- /update-settings: removed Gradio call, settings are applied at save time
- /save-dataset: migrated to REST API (/v1/dataset/save) which accepts
  tag_position and other settings directly as strings
- Frontend: pass dataset settings (tag, position, etc.) when saving

components/TrainingPanel.tsx

@@ -474,6 +474,10 @@ export const TrainingPanel: React.FC = () => {
       const result = await trainingApi.saveDataset({
         savePath: savePath || `./datasets/${datasetSettings.datasetName}.json`,
         datasetName: datasetSettings.datasetName,
+        customTag: datasetSettings.customTag,
+        tagPosition: datasetSettings.tagPosition,
+        allInstrumental: datasetSettings.allInstrumental,
+        genreRatio: datasetSettings.genreRatio,
       }, token);
       setSaveStatus(result.status as string);
       if (result.path) setSavePath(result.path);