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The squash-merge of PR #419 was performed against an outdated PR base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/pages/Settings.tsx

@@ -396,7 +396,7 @@ const SETTINGS_INDEX: SearchIndexEntry[] = [
   { tab: 'appearance',     titleKey: 'settings.uiScaleTitle',             keywords: 'ui scale zoom dpi size' },
   { tab: 'appearance',     titleKey: 'settings.font',                     keywords: 'font typography typeface' },
   { tab: 'appearance',     titleKey: 'settings.fsPlayerSection',          keywords: 'fullscreen player mesh blob' },
-  { tab: 'appearance',     titleKey: 'settings.seekbarStyle',             keywords: 'seekbar progress bar waveform' },
+  { tab: 'appearance',     titleKey: 'settings.seekbarStyle',             keywords: 'seekbar progress bar waveform reduced animations performance gpu fps low-end framerate cap' },
   { tab: 'input',          titleKey: 'settings.inputKeybindingsTitle',    keywords: 'keybindings shortcuts hotkeys keyboard' },
   { tab: 'input',          titleKey: 'settings.globalShortcutsTitle',     keywords: 'global shortcuts hotkeys system-wide media keys' },
   { tab: 'system',         titleKey: 'settings.language',                 keywords: 'language locale translation i18n' },
@@ -3844,6 +3844,16 @@ export default function Settings() {
                   />
                 ))}
               </div>
+              <div className="settings-toggle-row" style={{ marginTop: '1rem', paddingTop: '1rem', borderTop: '1px solid var(--border)' }}>
+                <div>
+                  <div style={{ fontWeight: 500 }}>{t('settings.reducedAnimations')}</div>
+                  <div style={{ fontSize: 12, color: 'var(--text-muted)' }}>{t('settings.reducedAnimationsDesc')}</div>
+                </div>
+                <label className="toggle-switch" aria-label={t('settings.reducedAnimations')}>
+                  <input type="checkbox" checked={auth.reducedAnimations} onChange={e => auth.setReducedAnimations(e.target.checked)} />
+                  <span className="toggle-track" />
+                </label>
+              </div>
             </div>
           </SettingsSubSection>