v0.17.0

Folder uploads, and a silent failure removed. One behaviour change worth reading
before upgrading: files-selected no longer fires for an empty selection.

Folder uploads, and the drop that used to vanish

box-drop-zone read dataTransfer.files, which the platform simply cannot use
to describe a directory. Dropping a folder produced an empty list, so the zone
reported nothing and the drop disappeared with no error and no rejection — the
worst kind of failure, because it looks like nothing happened.

The zone now reads the entry list instead, and reads it synchronously inside
the drop handler: the item list is emptied the moment that handler returns, so
awaiting anything before capturing it loses the drop. Traversal happens
afterwards, off the captured entries, batching through readEntries until it
comes back empty — the call caps at about 100 children, and reading it once is
how a 250-file folder silently becomes a 100-file folder. macOS packages
(.app, .rtfd) arrive as directories the OS also calls a zip; those upload
whole rather than being walked, which would scatter a bundle's internals.

files-selected now carries entries — each file with the directory it came
from — alongside the existing flat files list, which is unchanged, and
skipped, naming anything the browser refused to hand over. A drop or a
dismissed picker that carries no files now emits nothing at all, where it
previously announced an empty selection; a drop where everything was skipped
still reports, because that is a failure rather than silence.

Traversal never rejects. A directory that cannot be read yields the files read
before it failed, so one unreadable subfolder no longer discards the hundreds of
files around it — which it previously did as an unhandled rejection, losing the
whole drop.

box-content-uploader recreates the dropped tree through a new optional
createFolder on UploadTransport. It is optional because requiring it would
break every transport already written against the interface; a transport without
it refuses a folder drop with a new folder-unsupported rejection rather
than flattening the tree into the destination root, which has no undo. Folders
are created lazily, when a file in them actually starts uploading, and the
in-flight promise is shared, so two files racing into the same folder create it
once rather than making two folders with the same name. Because that request is
shared it belongs to the controller rather than to whichever file happened to
start it: cancelling one file cancels that file, not its siblings.

An interrupted folder upload does leave behind the folders it had already
created, some of them empty. There is no atomic "create this tree" underneath,
and an uploader deleting folders on a destination it does not own would be worse
than a stray empty one; a retry reuses them.

file-limit caps the queue, defaulting to 100 — matching box-ui-elements. A
default matters here in a way it did not before: a dropped folder can carry
thousands of files, and the queue had no back pressure at all. Files past the cap
are rejected with file-limit-reached.

box-drop-zone also gained accept, and the uploader now fills it in from
extensions, so the browse dialog stops offering files the queue would reject.
It is advisory only — a person can still pick "All files", and it does nothing
for a drop — so the queue's own check remains the real one.

Also on the uploader: directories turns click-to-browse into a folder picker
(dropped folders are read either way — the platform only forces the choice on the
browse path), addEntries() queues pathed files directly, and a burst of queue
events now coalesces into a single re-render, which a 100-file drop needs.