Replace the full-tree nuke-and-reload in refreshRoot() with a targeted
refreshDirectory(parentPath) that only evicts and reloads the single
parent directory whose contents changed.
Before: every create/rename/delete call cleared the entire childrenByDir
cache and reloaded only the root, causing all expanded subdirectories to
flash empty and visually reset.
After: only the parent directory of the affected entry is reloaded in-place;
every other expanded directory keeps its cached children, so the tree state
is preserved and there is no visible flash or scroll-position reset.
Applies to both FilesView and SidebarFilesTree.
Nguyễn Ngô Thượng
b4949c6e33