fix: name the allowed-paths action for what it adds, a path or a file

"Add folder or path" promised one thing and offered another: the listing is
folders only, because the Host's browse primitive has no file rows, while the
extras legitimately name files — `../../CONTROLLER.md` is the example the panel
itself gives.

The action is "Add path or file", its field is "Path or file", and the hint says
which of the two the list can show and how the other one is added. Nothing about
the interaction moved; the copy was the part that was wrong.

README.md

@@ -161,7 +161,8 @@ a breadcrumb trail, a hidden-entries toggle — driven through
 stored in the form that keeps its meaning: `/work/root/src/shared` becomes
 `src/shared` when the session started in `/work/root`. The picker's own path field
 stays editable, because the Host lists folders and an extra may legitimately name
-a file.
+a file — which is why that action reads **Add path or file** and its field **Path
+or file**, rather than promising a folder the list would then fail to show.
 
 Because the panel owns widening, `facet action=add` is the *other* path and the
 narrower one: it is gated on an approval channel, and a deployment with none — the