feat(i18n): add document processing confirmation dialog translations

- Add "processingDocuments" translation key for loading state message in English and Chinese
- Add "startUploadConfirmTitle" translation for confirmation dialog title
- Add "startUploadConfirmContent" translation for confirmation dialog description
- Add "returnToList" translation for returning to list page action
- Add "stayOnPage" translation for staying on current page action
- Support user choice to either return to list or stay on page during background document processing

web/src/i18n/en.ts

@@ -559,6 +559,7 @@ export const en = {
       fileName: 'File Name',
       fileList: 'File List',
       blockPreview: 'Block Preview',
+      processingDocuments: 'Processing documents, please wait...',
       chunkContent: 'Chunk Content',
       sampleChunk: 'Sample Chunk Content',
       noFilesSelected: 'No files',
@@ -568,6 +569,10 @@ export const en = {
       waiting: 'Waiting',
       startUpload: 'Total {{count}} files | Start Upload',
       startUploading: 'Start Uploading',
+      startUploadConfirmTitle: 'Start Processing Documents',
+      startUploadConfirmContent: 'Document processing will run in the background. You can choose to return to the list page immediately or stay on this page to view the processing progress.',
+      returnToList: 'Return to List',
+      stayOnPage: 'Stay on Page',
       uploadSuccess: 'Upload Success',
       datasetName: 'Dataset Name',
       pleaseEnterDatasetName: 'Please enter dataset name',