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/main.js

@@ -12,7 +12,7 @@ import {
   npToggleStar, updateMediaSession,
 } from './player.js';
 import {
-  navigate, _navGoBack, _navLoad, onLocalSearch, onMobileSearch,
+  navigate, _navGoBack, _navLoad, onHeaderSearch, closeHeaderSearch,
   onGlobalSearch, s_goArtist, s_goAlbum, playerBarGoArtist, playerBarGoAlbum,
   searchSimilarArtist, searchAndPreview, loadItunesAlbum, expandArtistBio,
   loadAlbums, loadStarred, loadRandom, filterStarred, filterPlaylist,
@@ -293,7 +293,7 @@ try { history.replaceState({ nsIdx: 0 }, '', ''); } catch {}
 // ─── EXPOSE GLOBALS (for HTML onclick attributes) ───
 Object.assign(window, {
   // Navigation
-  navigate, onLocalSearch, onMobileSearch, onGlobalSearch, s_goArtist, s_goAlbum,
+  navigate, onHeaderSearch, closeHeaderSearch, onGlobalSearch, s_goArtist, s_goAlbum,
   playerBarGoArtist, playerBarGoAlbum, searchSimilarArtist, searchAndPreview,
   loadItunesAlbum, expandArtistBio,
   // Player