fix(web): browser/mouse Forward navigation now works (not only Back)

The popstate listener always called _navGoBack(), but both Back and Forward fire
popstate — so Forward was treated as Back and never restored the page you came from.
_navGoBack also pushState()'d on every back, which wiped the browser's forward stack
entirely.

Route all history through the History API: navigate() pushes a state (nsIdx) only on
genuine new navigation; popstate now applies whichever entry the browser moved to via
_navOnPopState(state.nsIdx), covering Back AND Forward with no pushState in the
handler. In-app back buttons / Backspace go through history.back() so there's a single
path and the browser stack stays in sync. NowPlaying overlays still close first on a
back press.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/main.js

@@ -13,7 +13,7 @@ import {
   npToggleStar, updateMediaSession, updateNpColorMode, reconcileNativeState, initKeyboardShortcuts,
 } from './player/player.js';
 import {
-  navigate, _navGoBack, _navLoad, onHeaderSearch, closeHeaderSearch,
+  navigate, _navGoBack, _navOnPopState, _navLoad, onHeaderSearch, closeHeaderSearch,
   onGlobalSearch, s_goArtist, s_goAlbum, playerBarGoArtist, playerBarGoAlbum,
   searchSimilarArtist, searchAndPreview, loadItunesAlbum, closeEventsModal,
   loadAlbums, loadStarred, loadRandom, filterStarred, filterPlaylist,
@@ -299,7 +299,7 @@ window.addEventListener('load', () => {
   }
 });
 
-window.addEventListener('popstate', () => _navGoBack());
+window.addEventListener('popstate', (e) => _navOnPopState(e.state));
 document.addEventListener('keydown', e => {
   if(e.key !== 'Backspace') return;
   const t = document.activeElement?.tagName;