feat(banner): HLS motion-artwork header banners and audio-quality badges

Add a MotionHeaderBanner (video_player) that plays a looping muted HLS header video with a static image fallback for artist, album, and playlist screens. The Go backend now exposes header_video, header_image, and audio_traits from extensions. Album/playlist headers show the release year and Dolby Atmos / Lossless badges inline, full date and song count in a footer, a centered square cover when no video is present, and a full-bleed video when one is.

lib/widgets/motion_header_banner.dart

@@ -0,0 +1,131 @@
+import 'package:flutter/material.dart';
+import 'package:video_player/video_player.dart';
+import 'package:spotiflac_android/utils/logger.dart';
+
+final _log = AppLogger('MotionHeaderBanner');
+
+class MotionHeaderBanner extends StatefulWidget {
+  final String videoUrl;
+  final Widget fallback;
+  final BoxFit fit;
+  final Alignment alignment;
+
+  const MotionHeaderBanner({
+    super.key,
+    required this.videoUrl,
+    required this.fallback,
+    this.fit = BoxFit.cover,
+    this.alignment = Alignment.topCenter,
+  });
+
+  @override
+  State<MotionHeaderBanner> createState() => _MotionHeaderBannerState();
+}
+
+class _MotionHeaderBannerState extends State<MotionHeaderBanner>
+    with WidgetsBindingObserver {
+  VideoPlayerController? _controller;
+  bool _ready = false;
+  bool _failed = false;
+
+  @override
+  void initState() {
+    super.initState();
+    WidgetsBinding.instance.addObserver(this);
+    _initialize();
+  }
+
+  @override
+  void didUpdateWidget(MotionHeaderBanner oldWidget) {
+    super.didUpdateWidget(oldWidget);
+    if (oldWidget.videoUrl != widget.videoUrl) {
+      _disposeController();
+      _ready = false;
+      _failed = false;
+      _initialize();
+    }
+  }
+
+  Future<void> _initialize() async {
+    final url = widget.videoUrl.trim();
+    if (url.isEmpty) {
+      setState(() => _failed = true);
+      return;
+    }
+
+    final controller = VideoPlayerController.networkUrl(
+      Uri.parse(url),
+      formatHint: VideoFormat.hls,
+    );
+    _controller = controller;
+    try {
+      await controller.initialize();
+      if (!mounted) {
+        await controller.dispose();
+        return;
+      }
+      await controller.setVolume(0);
+      await controller.setLooping(true);
+      await controller.play();
+      setState(() => _ready = true);
+    } catch (e) {
+      _log.w('Failed to play motion banner: $e');
+      if (!mounted) return;
+      setState(() => _failed = true);
+    }
+  }
+
+  void _disposeController() {
+    final controller = _controller;
+    _controller = null;
+    controller?.dispose();
+  }
+
+  @override
+  void didChangeAppLifecycleState(AppLifecycleState state) {
+    final controller = _controller;
+    if (controller == null || !_ready) return;
+    if (state == AppLifecycleState.resumed) {
+      controller.play();
+    } else if (state == AppLifecycleState.paused ||
+        state == AppLifecycleState.inactive) {
+      controller.pause();
+    }
+  }
+
+  @override
+  void dispose() {
+    WidgetsBinding.instance.removeObserver(this);
+    _disposeController();
+    super.dispose();
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    final controller = _controller;
+    final showVideo = _ready && !_failed && controller != null;
+
+    return Stack(
+      fit: StackFit.expand,
+      children: [
+        widget.fallback,
+        AnimatedOpacity(
+          opacity: showVideo ? 1.0 : 0.0,
+          duration: const Duration(milliseconds: 400),
+          child: showVideo
+              ? FittedBox(
+                  fit: widget.fit,
+                  alignment: widget.alignment,
+                  clipBehavior: Clip.hardEdge,
+                  child: SizedBox(
+                    width: controller.value.size.width,
+                    height: controller.value.size.height,
+                    child: VideoPlayer(controller),
+                  ),
+                )
+              : const SizedBox.shrink(),
+        ),
+      ],
+    );
+  }
+}