Audiobooks: talk to OpenAudible directly with its own username and password (OPENAUDIBLE_URL)

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

public/settings.js

@@ -80,7 +80,7 @@ function viewSettings() {
     </div>
     ${signed ? '<div class="bar"><button class="btn danger" id="out">Sign out of Seafile</button></div>' : ''}</div>
     <div id="sec-mail"><h2>Mail</h2><div class="list" id="mailst"><div class="row"><span class="grow"><small>Checking…</small></span></div></div></div>
-    <div id="sec-audio"><h2>Audiobooks sign-in</h2><p class="sub">Saved on your server (encrypted) and shared with all your devices. Leave blank to skip. Use the copy button on the Audiobooks tab to paste them into the site's sign-in form.</p>
+    <div id="sec-audio"><h2>Audiobooks sign-in</h2><p class="sub">Your OpenAudible username and password (the server's audiobook library login). Saved on your server (encrypted) and shared with all your devices. The Audiobooks tab uses them to load your library and play books.</p>
     <div class="card" style="max-width:none"><label for="ab-u">Username</label>
       <input type="text" id="ab-u" autocomplete="off" autocapitalize="off" value="${esc(abCreds().u)}">
       <label for="ab-p">Password</label>