feat(ui): add sortable column headers to the file list

[huelsmc]

Summary

The file browser had no column headers, so a long listing could not be reordered. This adds a sticky header row (Name, Size, Last modified) where clicking a header sorts by that column.

Behaviour

• Clicking the active column flips between ascending and descending; clicking a different column starts ascending. A chevron marks the active column, and aria-sort is set on the header cells.
• The default is name, ascending. Names sort naturally and ignore case (file2 before file10).
• Folders always stay above files. They have no size or date, so they keep name order when sorting by size or date.
• Files without a date stay at the bottom when sorting by date, in either direction.
• The header stays visible while scrolling and supports dark mode.
• Folder action buttons now have their own right-hand column, so they no longer sit under "Last modified".
• Header labels are translated in all six locales (en, de, fr, pl, nl, ro).

Note

Sorting is client-side and covers the pages loaded so far. In folders with more than 1,000 objects, the order updates when "Load more" fetches the next page.

Changes

• src/renderer/lib/sortEntries.ts (new, with unit tests): pure sort logic and header toggle state.
• src/renderer/components/files/FileBrowser.tsx: header row and sorted listing.
• FileBrowser.test.tsx: header click and aria-sort tests.
• src/renderer/i18n/locales/*.json: four new files.column* keys per locale.

Testing

• npm run lint passes with no new warnings, npm run typecheck passes, and npm test passes (602 tests).
• Checked manually in the dev build (npm start) against a real bucket.

🤖 Generated with Claude Code

https://claude.ai/code/session_01RR6wV54o4jV23tysVcT8HK