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 (auto-fetched from TMDB)
  • Editable title field
  • Editable poster URL field
  • Category selector
  • Delete button to remove from batch
• Duplicate detection: Each file's infohash is parsed client-side and compared against existing torrents in DB. Duplicates are highlighted with a warning ("already in database") and fields are pre-filled from existing data
• Unified flow: Both single and multiple file uploads use the same list-based UI for consistency

Bug fixes

• Card jumping fix: Torrent list now uses useMemo with stable sort (timestamp + hash tiebreaker) to prevent cards from reordering on each 1-second refetch. The backend returns torrents in non-deterministic order when timestamp and title are equal
• Sort comparator fix: Replaced broken (a, b) => a.title > b.title (returns boolean, causes unstable sort) with localeCompare
• Grid stability: Replaced minmax(max-content, 570px) with minmax(450px, 570px) to prevent layout shifts from dynamic content
• TorrentCard memo optimization: Custom comparator checks only visible fields (hash, title, name, poster, category, stat, size, speed, data) instead of shallow object comparison, preventing unnecessary re-renders every second
• Crash fix: Added null guards for torrents before .map()/.filter() calls (undefined on initial render before query resolves)

Code cleanup

• Removed dead code: LeftSideBottomSectionFileSelected, TorrentIconWrapper, CancelIconWrapper styled-components; unused hashRegex export; commented-out catArray
• Simplified AddDialog: file upload logic moved entirely to MultiAddDialog, AddDialog now only handles link/magnet/hash and edit mode
• Simplified LeftSideComponent: removed "file selected" state, dropzone always visible
• Backend: removed dead multiFile title/poster blanking logic in upload.go (frontend now sends one request per file)

Localization

• Updated ClickOrDrag text in all 7 locales to indicate multiple file support (e.g., "CLICK / DRAG & DROP FILES (.torrent)")

Test plan

• Drop single .torrent file — MultiAddDialog opens with one item, fields editable
• Drop multiple .torrent files — all shown in scrollable list with individual fields
• Drop already-added .torrent — warning shown, fields pre-filled from DB
• Add via magnet/hash/link — original AddDialog flow unchanged
• Edit existing torrent — edit dialog unchanged
• Verify torrent cards don't jump/reorder 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