v0.5.51

feat(sidebar): sort duplicates inside a folder by drag and drop

Nested duplicates rendered as plain rows, so they could not be dragged at all,
and their order never reached settings.projectOrder — every refresh put them
back in filesystem order.

- every project row is a sortable item now; a dragged duplicate only changes
  places with its siblings, and dropping it on its parent sends it to the top,
  while the rest of the list stays put instead of shifting under the pointer
- projectOrder trails each project with its nested duplicates, which is what
  makes the order survive: the backend keeps the relative order of the copies
  it regroups after their parent
- each row carries its own piece of the folder tree inside its sortable box, so
  a live drag moves the lines with the rows instead of stranding them, and no
  folder has to blank its connectors while a drag is in progress