fix: restore audio refactor + features lost in #419 squash-merge (#429)

The squash-merge of PR #419 was performed against an outdated PR base
that predated several main-side refactors and features. The resulting
squash inadvertently re-introduced files that had already been removed
(`src-tauri/src/audio.rs` monolith, `app-icon.png`) and reverted main's
content for ~20 files (`src-tauri/src/lib.rs` decompose, `src/App.tsx`
animation-pause, `src/components/AlbumRow.tsx` headerExtra, etc).

This commit:

* Restores all collateral-damage files to their pre-#419 main state
  (5662dafe), including the audio module split, lib decompose,
  Cargo.toml `windows` dep, animation-pause-on-blur logic, and
  `reducedAnimations` toggle plumbing in WaveformSeek/Settings.
* Keeps the genuine #419 work intact: tri-state duration toggle,
  position counter, persistent Now Playing collapse, animated EQ
  indicator (in QueuePanel.tsx, 8 locales, authStore, components.css).
* Merges authStore.ts so both `reducedAnimations` (from #426) and
  `queueNowPlayingCollapsed` (from #419) coexist.
* Adds the `.eq-bars.paused` CSS rule manually since components.css
  needed a 5662dafe base + the single #419 addition.
* Fixes a latent type error in OverlayScrollArea.tsx (`useRef<T>(null)`
  is `RefObject<T>` / read-only under current `@types/react`; widened to
  `useRef<T | null>(null)` so the existing `wrapRef.current = el`
  assignment compiles).

Verified locally with `cargo check` and `npm run build` — both green.

src/components/PlayerBar.tsx

@@ -237,6 +237,7 @@ export default function PlayerBar() {
   const playSlotRef = useRef<HTMLSpanElement>(null);
   const scheduleRemaining = usePlaybackScheduleRemaining();
   const isPreviewing = usePreviewStore(s => s.previewingId !== null);
+  const previewAudioStarted = usePreviewStore(s => s.audioStarted);
   const previewingTrack = usePreviewStore(s => s.previewingTrack);
 
   const isRadio = !!currentRadio;
@@ -312,7 +313,7 @@ export default function PlayerBar() {
     <>
     <footer
       ref={playerBarRef}
-      className={`player-bar ${floatingPlayerBar ? 'floating' : ''}${showPreviewMeta ? ' is-previewing' : ''}`}
+      className={`player-bar ${floatingPlayerBar ? 'floating' : ''}${showPreviewMeta ? ' is-previewing' : ''}${showPreviewMeta && previewAudioStarted ? ' audio-started' : ''}`}
       style={floatingPlayerBar ? floatingStyle : undefined}
       role="region"
       aria-label={t('player.regionLabel')}