cloud.py: list_connections now decrypts and surfaces server_url +
connection_username for nextcloud/webdav providers; folder route uses
{folder_id:path} to handle slashes; translates "root" sentinel to "".
nextcloud_backend.py: skip parent directory entry in PROPFIND Depth:1 results.
webdav_backend.py: add cloud_folder + original_filename params to
upload_object so files land in the user's chosen folder with their real name.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>