Summary

Replaces the indeterminate "Batch download has started..." snackbar with a real-time progress tracker for browser-side batch downloads.

Before

• Indeterminate spinner with no progress information
• "Details" button opens a text log
• No warning when closing tab during download
• No feedback on completion or cancellation

After

• File counter: "3 / 76 files downloaded (2%)"
• Byte-based progress bar that updates smoothly during large file downloads
• Current filename being downloaded (with "saving..." status during disk write)
• Download speed in MB/s (rolling 5-sample average)
• Total bytes downloaded
• Cancel button (red X) that cleanly aborts the download
• Green "Download complete!" toast with file count and total size on success
• Yellow "Download cancelled" toast when user cancels
• Browser beforeunload warning to prevent accidental tab closure during downloads

How it works

• Streams each fetch response via ReadableStream.getReader() to count bytes in real-time
• Walks the file tree upfront to calculate total expected bytes for accurate percentage
• Throttles Redux dispatches to every 500ms to avoid render storms
• Uses the existing cancelSignals AbortController for clean cancellation
• Uses the existing LoadingSnackbar getProgress callback for the circular progress indicator

Files changed

| File | Change |
| src/redux/thunks/download.ts | Progress tracking, byte streaming, cancel/complete handling |
| src/component/Common/Snackbar/snackbar.tsx | Progress and completion UI components |
| src/redux/globalStateSlice.ts | BatchDownloadProgress state and reducers |
| src/component/Common/Snackbar/LoadingSnackbar.tsx | Layout adjustment for progress display |
| src/redux/thunks/file.ts | Added getProgress param to longRunningTaskWithSnackbar |
| public/locales/en-US/application.json | i18n strings for new UI text |

Test plan

• Select multiple files → Download → Browser-side download to folder
• Verify progress bar, file counter, speed, and current filename update in real-time
• Verify large files show "(saving...)" status during disk write
• Click cancel during download → verify download stops and "Download cancelled" toast appears
• Let download complete → verify "Download complete!" toast with summary
• Try closing/refreshing tab during download → verify browser "Leave site?" warning
• Verify existing download log dialog still works via "Details" button