feat: multi-file torrent upload with per-file editing

[staners2]

Summary

Adds support for selecting and uploading multiple .torrent files at once, with a dedicated dialog for editing each file's metadata before saving.

New functionality

• Multi-file upload: Dropzone now accepts multiple .torrent files (drag & drop or file picker)
• MultiAddDialog: When files are selected, a new dialog displays all files as a scrollable list. Each file has:
  • Poster thumbnail with index number (auto-fetched from TMDB)
  • Editable title field (pre-filled with filename without .torrent extension)
  • Editable poster URL field
  • Category selector
  • Delete button to remove from batch
• Duplicate filtering: Each file's infohash is parsed client-side and compared against existing torrents in DB. Duplicates are silently filtered out — only new torrents are shown and uploaded
• Unified flow: Both single and multiple file uploads use the same list-based UI
• Card separation: Each file displayed as a distinct card with border-radius, shadow and spacing

Code changes

• New MultiAddDialog component with styled-components (MultiFileRow, MultiFilePoster, MultiFileInfo, MultiFileList)
• Simplified AddDialog: file uploads delegated to MultiAddDialog, handles only link/magnet/hash and edit mode
• Simplified LeftSideComponent: no "file selected" state, dropzone always visible
• Backend upload.go: cleaned up dead multiFile title/poster blanking logic
• Stable torrent list sort via useMemo (timestamp + hash tiebreaker)
• TorrentCard memo optimization with custom comparator for visible fields
• Grid layout fix: minmax(450px, 570px) instead of unstable minmax(max-content, 570px)
• Null guards for torrents before .map()/.filter() (crash fix on initial render)
• Removed dead code: LeftSideBottomSectionFileSelected, TorrentIconWrapper, CancelIconWrapper, unused hashRegex export
• Updated ClickOrDrag text in all 7 locales for multiple file support

Test plan

• Drop single .torrent file — list with one editable item
• Drop multiple .torrent files — all shown with individual fields and correct numbering
• Drop already-added .torrent files — duplicates filtered out, only new shown
• All files are duplicates — dialog closes (nothing to add)
• Add via magnet/hash/link — original flow unchanged
• Edit existing torrent — edit dialog unchanged
• Verify cards don't jump after adding
• Test on narrow screen (<700px) — dialog goes fullscreen

[pavelpikta]

Hi @staners2
Don't need to push chages for static files, static files will udpated before release

[staners2]

Does this multi-add visualization work — separating items into "to be added" and "already in database" sections — or do you have any suggestions for a better approach?

[pavelpikta]

Работает ли эта визуализация с множеством добавлений — разделение элементов на разделы «для добавления» и «уже в базе данных» — или у вас есть предложения по лучшему подходу?

how about to skip torrents that already in database and show only torrents that will be added?

[staners2]

Done. Torrents that are already in the database are now skipped, and only the ones to be added are displayed.