chore: remove unused showSetupError from ui.js (duplicate of _showSetupError in main.js)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/ui.js

@@ -50,11 +50,6 @@ export function switchSetupTab(t) {
   document.querySelectorAll('.setup-tab').forEach((el,i)  => el.classList.toggle('active', i===(t==='navidrome'?0:1)));
   document.querySelectorAll('.setup-pane').forEach((el,i) => el.classList.toggle('active', i===(t==='navidrome'?0:1)));
 }
-export function showSetupError(m) {
-  const el = document.getElementById('setup-error');
-  el.textContent = m; el.style.display = 'block';
-}
-
 // ─── SETTINGS ───
 export function openSettings() {
   // Lazy import to avoid circular dep — abs.js imports views.js