Drive: shortcuts, selection, sorting, clipboard, file creation, full-window drop

Adds a much more keyboard- and mouse-native workspace:
- Ctrl/Cmd+K command palette (fuzzy search across folders/spaces, files in the
  open folder, and quick actions) plus a '?' shortcut cheat-sheet.
- Keyboard: arrows to navigate, Enter to open, Backspace/Alt+Left to go up,
  Delete to trash, F2 to rename, Ctrl+A select-all, Esc to clear.
- Click anywhere on a row/card selects it (name still opens); Ctrl/Cmd+click
  toggles, Shift+click ranges. Selection toolbar with bulk download/move/delete.
- Sortable columns (name/size/modified), persisted with the grid/list choice.
- Copy/Cut/Paste + Duplicate for normal spaces (Ctrl+C/X/V/D). Vault files have
  no server-side move/copy, so clipboard/bulk-move are normal-space only; delete
  and download work everywhere.
- New empty file creation (opens straight in the editor for normal spaces).
- Full-window drag & drop with a clear 'drop your files here' overlay.

New components: drive/DropOverlay, drive/CommandPalette, drive/ShortcutsHelp.
FR/EN strings kept in parity (388 each).

Author: softpython2884