Live test B1: the Folder list indented a server list sorted as full-path
text, so "-" and "_" sorted before "/" and children landed under the wrong
parent (kiko/char under kiko-v6), with case variants interleaved. The
options are now a tree built by segment: each folder directly under its own
parent, case variants distinct siblings.
On POSIX a folder named "Metadata\Klein..." was listed but filtered to no
prompts, because normalize_folder read "\" as a separator. It now does so
only on Windows (ntpath), as the listing already did.
Refs #444