Files: sturdier Seafile pass-through (timeouts, retries, stop on disconnect), in-place sign-in, saved folder lists, upload name clashes, undo and recycle bin, library search, zip downloads, share link options, text viewer and editor

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

public/index.html

@@ -70,6 +70,7 @@
 <script src="/lyrics-view.js"></script>
 <script src="/settings.js"></script>
 <script src="/files.js"></script>
+<script src="/files-extra.js"></script>
 <script src="/sheets.js"></script>
 <script src="/file-actions.js"></script>
 <script src="/signal-view.js"></script>