android: a folder of audio files, and a paste of track links

The paste door now reads itself the way the desktop's does: one track link
in the paste and every line is looked up on its own public page
(playlist_import_track_links), which is the way past Spotify's 100-track
public ceiling — the wait screen counts them as they arrive. A fourth door
imports a folder of audio files off this phone, picked with the storage
plugin's own document-tree picker; playlist_import_folder grew a path
argument for it, because on Android it had no dialog to open and always
answered nothing. A YouTube playlist link needed no door at all — the link
one already dispatches it.

src/lib/api.js

@@ -278,7 +278,9 @@ export const playlistCoverSet = (id, path) => invoke("playlist_cover_set", { id,
 // Import: probe opens a file dialog and stages a reviewed draft; text stages
 // a pasted tracklist; commit writes the accepted draft in one transaction.
 export const playlistImportProbe = () => invoke("playlist_import_probe");
-export const playlistImportFolder = () => invoke("playlist_import_folder");
+// The desktop opens its own folder dialog (no path); the phone picks with
+// the storage plugin and hands the resolved path in.
+export const playlistImportFolder = (path = null) => invoke("playlist_import_folder", { path });
 export const playlistImportText = (text) => invoke("playlist_import_text", { text });
 export const playlistImportYoutube = (url) => invoke("playlist_import_youtube", { url });
 export const playlistImportYoutubePlaylist = (url) =>