feat(file-tree): add ⋯ menu button on each row to open the context menu

Touch devices don't get a free way to open the file-tree context menu now
that the long-press gesture is reserved for drag. Add a small horizontal
three-dots button (MoreHorizontal) on the right of every file, folder,
and workspace-root row. Clicking it dispatches a synthetic contextmenu
MouseEvent on the row so Radix's existing ContextMenuTrigger opens the
same menu the right-click and long-press paths open — no menu items
duplicated.

- FileTreeFile / FileTreeFolder gain an optional actions?: ReactNode prop
  rendered inside the existing FileTreeActions wrapper (which already
  stops click bubbling).
- RowMoreButton (new component) walks up to the nearest
  [data-tree-row-path] ancestor and dispatches the contextmenu event.
- Folder.fileTreeTab.moreActions added to all 10 locales.
- useLongPressToOpenMenu is kept (and its tests restored) for reuse
  elsewhere; the file tree now relies on the more button + native
  right-click instead of the long-press hook.