v2.50.1 — Player-Glow an Akzent + Pulsation, Cover-Crossfade, existsSync-Fix

## Fullscreen-Player (now_playing_screen.dart)
- Glow-Farbe folgt MeloTheme.akzentNotifier (Per-User-Akzent) statt fixem Rot; Listener rebuildet bei Akzentwechsel
- Dynamische Glow-Pulsation: AnimationController (Bordmittel) pulsiert blurRadius 50–70 / spreadRadius 6–12 nur bei Wiedergabe, stillstehend bei Pause
- Blur-Hintergrund crossfaded beim Songwechsel (AnimatedSwitcher 600ms, layoutBuilder mit StackFit.expand, ValueKey je Song)
- existsSync aus dem Build-Pfad entfernt: async _ladeCoverStatus mit try/catch, Guard gegen stale Song-Wechsel

lib/screens/now_playing_screen.dart

@@ -21,7 +21,8 @@ class NowPlayingScreen extends StatefulWidget {
   State<NowPlayingScreen> createState() => _NowPlayingScreenState();
 }
 
-class _NowPlayingScreenState extends State<NowPlayingScreen> {
+class _NowPlayingScreenState extends State<NowPlayingScreen>
+    with SingleTickerProviderStateMixin {
   final PlayerService _player = PlayerService();
   final FavoritenService _favoriten = FavoritenService();
   final LyricsService _lyricsService = LyricsService();
@@ -51,9 +52,21 @@ class _NowPlayingScreenState extends State<NowPlayingScreen> {
   bool _istFavorit = false;
   bool _toggleLaeuft = false; // In-Flight-Guard gegen Doppel-Tap-Race
 
+  // ─── Glow-Pulsation (synchron zum Play-Zustand) ───
+  late final AnimationController _glowController;
+
+  // ─── Cover-Prüfung (async, kein existsSync im Build-Pfad) ───
+  bool _hatCover = false;
+  String? _coverPfad;
+
   @override
   void initState() {
     super.initState();
+    _glowController = AnimationController(
+      vsync: this,
+      duration: const Duration(milliseconds: 1400),
+    );
+    MeloTheme.akzentNotifier.addListener(_onAkzentGeaendert);
     _posSub = _player.positionStream.listen((pos) {
       if (!mounted) return;
       setState(() => _position = pos);
@@ -67,6 +80,7 @@ class _NowPlayingScreenState extends State<NowPlayingScreen> {
             ? _player.dauer
             : Duration.zero;
       });
+      _syncGlowPulsation();
     });
     _songSub = _player.onSongWechsel.listen((song) {
       if (!mounted || song == null) return;
@@ -80,6 +94,7 @@ class _NowPlayingScreenState extends State<NowPlayingScreen> {
       });
       _ladeLyricsFuer(song, _ladeGeneration);
       _ladeFavoritStatus(song);
+      _ladeCoverStatus(song);
     });
     _player.addListener(_onPlayerChanged);
     // Initialen Zustand laden (falls schon ein Song läuft)
@@ -88,18 +103,22 @@ class _NowPlayingScreenState extends State<NowPlayingScreen> {
       _ladeGeneration++;
       _ladeLyricsFuer(song, _ladeGeneration);
       _ladeFavoritStatus(song);
+      _ladeCoverStatus(song);
     }
+    _syncGlowPulsation();
     _syncSleepTick();
   }
 
   @override
   void dispose() {
     _player.removeListener(_onPlayerChanged);
+    MeloTheme.akzentNotifier.removeListener(_onAkzentGeaendert);
     _posSub?.cancel();
     _stateSub?.cancel();
     _songSub?.cancel();
     _sleepTick?.cancel();
     _scrollController.dispose();
+    _glowController.dispose();
     super.dispose();
   }
 
@@ -108,9 +127,53 @@ class _NowPlayingScreenState extends State<NowPlayingScreen> {
   void _onPlayerChanged() {
     if (!mounted) return;
     setState(() {});
+    _syncGlowPulsation();
     _syncSleepTick();
   }
 
+  void _onAkzentGeaendert() {
+    if (mounted) setState(() {});
+  }
+
+  /// Glow-Pulsation: nur bei Wiedergabe animieren, bei Pause stillstehen.
+  void _syncGlowPulsation() {
+    if (_spielt) {
+      if (!_glowController.isAnimating) {
+        _glowController.repeat(reverse: true);
+      }
+    } else if (_glowController.isAnimating) {
+      _glowController.stop();
+      _glowController.value = 0; // Ruheposition (kleinster Glow)
+    }
+  }
+
+  /// Prüft asynchron, ob die Cover-Datei existiert (statt existsSync im
+  /// Build-Pfad — vermeidet UI-Jank). try/catch gegen Dateisystem-Fehler.
+  Future<void> _ladeCoverStatus(Song song) async {
+    final pfad = song.coverPfad;
+    if (pfad == null) {
+      if (mounted) {
+        setState(() {
+          _hatCover = false;
+          _coverPfad = null;
+        });
+      }
+      return;
+    }
+    bool existiert;
+    try {
+      existiert = await File(pfad).exists();
+    } catch (e) {
+      MeloLogger().fehler('cover_pfad_check', e);
+      existiert = false;
+    }
+    if (!mounted || _player.aktuellerSong?.coverPfad != pfad) return;
+    setState(() {
+      _hatCover = existiert;
+      _coverPfad = pfad;
+    });
+  }
+
   void _syncSleepTick() {
     final aktiv = _player.sleepTimerAktiv;
     if (aktiv && _sleepTick == null) {
@@ -435,7 +498,21 @@ class _NowPlayingScreenState extends State<NowPlayingScreen> {
       body: Stack(
         fit: StackFit.expand,
         children: [
-          _hintergrundBlur(song),
+          // Blur-Hintergrund mit Crossfade beim Songwechsel (Muster wie
+          // Cover↔Lyrics-Toggle, nur länger für weichen Übergang).
+          AnimatedSwitcher(
+            duration: const Duration(milliseconds: 600),
+            layoutBuilder: (currentChild, previousChildren) => Stack(
+              fit: StackFit.expand,
+              children: [
+                ...previousChildren,
+                if (currentChild != null) currentChild,
+              ],
+            ),
+            transitionBuilder: (child, anim) =>
+                FadeTransition(opacity: anim, child: child),
+            child: _hintergrundBlur(song),
+          ),
           // Abdunklung für Lesbarkeit
           const DecoratedBox(
             decoration: BoxDecoration(
@@ -473,12 +550,13 @@ class _NowPlayingScreenState extends State<NowPlayingScreen> {
   }
 
   /// Blur-Hintergrund aus dem Cover (Bordmittel: ImageFiltered + dart:ui).
+  /// Existenz-Check kommt aus dem async geladenen [_hatCover]/[_coverPfad] —
+  /// kein synchrones existsSync im Build-Pfad.
   Widget _hintergrundBlur(Song? song) {
-    final hatCover = song != null &&
-        song.coverPfad != null &&
-        File(song.coverPfad!).existsSync();
-    if (!hatCover) {
+    final pfad = _coverPfad;
+    if (!_hatCover || pfad == null) {
       return const DecoratedBox(
+        key: ValueKey('kein-cover'),
         decoration: BoxDecoration(
           gradient: LinearGradient(
             begin: Alignment.topCenter,
@@ -489,8 +567,9 @@ class _NowPlayingScreenState extends State<NowPlayingScreen> {
       );
     }
     return ImageFiltered(
+      key: ValueKey('cover-${song?.id ?? pfad}'),
       imageFilter: ImageFilter.blur(sigmaX: 45, sigmaY: 45),
-      child: Image.file(File(song.coverPfad!), fit: BoxFit.cover),
+      child: Image.file(File(pfad), fit: BoxFit.cover),
     );
   }
 
@@ -546,9 +625,7 @@ class _NowPlayingScreenState extends State<NowPlayingScreen> {
 
   /// Cover-Ansicht: großes Cover (Radius 20 + Glow), Titel, Künstler, Like.
   Widget _coverAnsicht(Song? song) {
-    final hatCover = song != null &&
-        song.coverPfad != null &&
-        File(song.coverPfad!).existsSync();
+    final hatCover = _hatCover && _coverPfad != null;
     final coverGroesse =
         (MediaQuery.of(context).size.width * 0.72).clamp(220.0, 340.0);
 
@@ -567,16 +644,17 @@ class _NowPlayingScreenState extends State<NowPlayingScreen> {
               borderRadius: BorderRadius.circular(20),
               boxShadow: [
                 BoxShadow(
-                  color: MeloTheme.rot.withValues(alpha: 0.45),
-                  blurRadius: 60,
-                  spreadRadius: 6,
+                  // Glow in der Akzentfarbe des Users, pulsierend bei Wiedergabe
+                  color: MeloTheme.akzent.withValues(alpha: 0.45),
+                  blurRadius: 50 + 20 * _glowController.value, // 50–70
+                  spreadRadius: 6 + 6 * _glowController.value, // 6–12
                 ),
               ],
             ),
             child: ClipRRect(
               borderRadius: BorderRadius.circular(20),
               child: hatCover
-                  ? Image.file(File(song.coverPfad!), fit: BoxFit.cover)
+                  ? Image.file(File(_coverPfad!), fit: BoxFit.cover)
                   : Container(
                       color: MeloTheme.rotHell,
                       child: const Icon(Icons.music_note,