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/mobile/Mobile.svelte

@@ -47,7 +47,7 @@
     import { resolver, streamSong, streamCatalogAlbum } from "./resolve.svelte.js";
     import { notice, clearNote } from "./notice.svelte.js";
     import * as pls from "./playlists.svelte.js";
-    import { importer, bindImporter } from "./importer.svelte.js";
+    import { importer, bindImporter, startFolder } from "./importer.svelte.js";
     import { bindShare } from "./share.svelte.js";
     import { downloadsAllowed, cellular } from "./network.svelte.js";
     import { contacts, loadContacts, display } from "./contacts.svelte.js";
@@ -197,7 +197,7 @@
         setTimeout(() => { api.libraryArtPrewarm([360]).catch(() => {}); }, 8000);
         /* the probe handle — the desktop has __soulstream for the same reason:
            tests/mobile/smoke.mjs drives the real app through it */
-        window.__ss = { nav, top, go, push, back, openSheet, closeSheet, openHalf, closeHalf, player, lib, art, slsk, net, resolver, streamSong, streamCatalogAlbum, sources, api, transfers, pls, notice, importer, wifi: { downloadsAllowed, cellular }, next, prev, toggle, seekSecs, playQueueAt, patch, contacts, loadContacts };
+        window.__ss = { nav, top, go, push, back, openSheet, closeSheet, openHalf, closeHalf, player, lib, art, slsk, net, resolver, streamSong, streamCatalogAlbum, sources, api, transfers, pls, notice, importer, imp: { startFolder }, wifi: { downloadsAllowed, cellular }, next, prev, toggle, seekSecs, playQueueAt, patch, contacts, loadContacts };
         return () => { if (unlisten) unlisten(); };
     });
 </script>