Replaced the hidden dropzone-only progress bar with a floating
upload toast that appears at the bottom-right corner whenever
files are being uploaded (button or drag-and-drop).
Features:
- Per-file progress bar with real byte-level tracking via XHR
- Spinning icon while uploading, green check on success, red on error
- Overall progress bar and file counter in the footer
- Auto-hides 4 seconds after all uploads complete
- Dismiss button to minimise the toast
- Works for both file and folder uploads
- i18n keys added to all 8 locale files
- Service worker cache bumped to v3
Dionisio