feat: persistent inline header search with overlay results

Replaces the hidden toggle-based mobile search bar with a permanently
visible pill-shaped search input in the header row, next to the logo.

- Search is always visible — no button click required
- Typing shows a floating overlay with library results (artists, albums,
  songs) without navigating away from the current page
- Clearing the input or navigating to any page closes the overlay silently
- The ✕ clear button appears only while text is present
- navigate() now calls closeHeaderSearch() so results disappear cleanly
  when tapping any result or bottom nav tab
- Old toggleMobileSearch / closeMobileSearch kept as no-op stubs for safety

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

src/ui.js

@@ -25,24 +25,12 @@ export function switchNavMode(mode) {
   document.getElementById('bnav-tab-discover')?.classList.toggle('active', mode==='discover');
 }
 
-// ─── MOBILE SEARCH ───
+// ─── MOBILE SEARCH (legacy stubs — header search is now always visible) ───
 export function toggleMobileSearch() {
-  const bar = document.getElementById('mobile-search-bar');
-  const btn = document.getElementById('mobile-search-btn');
-  const open = bar.style.display==='none' || bar.style.display==='';
-  bar.style.display = open ? 'block' : 'none';
-  btn.style.color   = open ? 'var(--accent)' : 'var(--text2)';
-  if(open) { setTimeout(() => document.getElementById('mobile-search-input').focus(), 50); }
-  else { closeMobileSearch(); }
+  document.getElementById('header-search-input')?.focus();
 }
 export function closeMobileSearch() {
-  const bar = document.getElementById('mobile-search-bar');
-  const inp = document.getElementById('mobile-search-input');
-  const btn = document.getElementById('mobile-search-btn');
-  bar.style.display = 'none';
-  btn.style.color   = 'var(--text2)';
-  inp.value = '';
-  navigate('home');
+  import('./views.js').then(m => m.closeHeaderSearch());
 }
 
 // ─── SETUP ───