Files like Finder, richer mini player, in-app Back/Forward, Audio tab renamed Audiobooks

- Files: multi-select, batch move/copy/delete, rename checks, sort, filter, shortcuts, drag in (files and folders) to upload with progress and retries, drag to move, drag a file out to download
- Mini player: previous, seek bar with buffered range, time, shuffle/repeat, buffering spinner, swipe for next/previous, close
- Back/Forward bar that knows what history is possible
- Audio tab is now Audiobooks

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

public/index.html

@@ -49,7 +49,7 @@
 <body>
 <div id="shell">
   <nav id="nav" aria-label="Main"></nav>
-  <div id="main"><main id="view"></main><div id="audiowrap" class="off"></div><div id="player" hidden></div></div>
+  <div id="main"><div id="navbar" hidden></div><main id="view"></main><div id="audiowrap" class="off"></div><div id="player" hidden></div></div>
 </div>
 <div id="toast" role="status"></div>
 <script src="/webauthn.js"></script>