new: language auto-detect - /api/guess-language, refresh button, guess on paste

web/static/app.css

@@ -178,3 +178,5 @@ td a.slug:hover { color: var(--accent); }
 .center .btn { width: 100%; margin-top: 12px; }
 .err { display: none; margin-top: 12px; font-size: 12.5px; color: #ff8fa3; }
 .center .foot { font-size: 12px; color: var(--muted-fg); padding: 14px; border-top: 1px solid var(--border); }
+
+.btn-icon { padding: 6px 10px; font-size: 14px; line-height: 1; }